Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1 | <?xml version="1.0" encoding="UTF-8"?> |
| 2 | <!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" |
| 3 | "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> |
| 4 | |
| 5 | <book id="libataDevGuide"> |
| 6 | <bookinfo> |
| 7 | <title>libATA Developer's Guide</title> |
| 8 | |
| 9 | <authorgroup> |
| 10 | <author> |
| 11 | <firstname>Jeff</firstname> |
| 12 | <surname>Garzik</surname> |
| 13 | </author> |
| 14 | </authorgroup> |
| 15 | |
| 16 | <copyright> |
Jeff Garzik | 4f93137 | 2006-09-29 05:07:25 -0400 | [diff] [blame] | 17 | <year>2003-2006</year> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 18 | <holder>Jeff Garzik</holder> |
| 19 | </copyright> |
| 20 | |
| 21 | <legalnotice> |
| 22 | <para> |
| 23 | The contents of this file are subject to the Open |
| 24 | Software License version 1.1 that can be found at |
| 25 | <ulink url="http://www.opensource.org/licenses/osl-1.1.txt">http://www.opensource.org/licenses/osl-1.1.txt</ulink> and is included herein |
| 26 | by reference. |
| 27 | </para> |
| 28 | |
| 29 | <para> |
| 30 | Alternatively, the contents of this file may be used under the terms |
| 31 | of the GNU General Public License version 2 (the "GPL") as distributed |
| 32 | in the kernel source COPYING file, in which case the provisions of |
| 33 | the GPL are applicable instead of the above. If you wish to allow |
| 34 | the use of your version of this file only under the terms of the |
| 35 | GPL and not to allow others to use your version of this file under |
| 36 | the OSL, indicate your decision by deleting the provisions above and |
| 37 | replace them with the notice and other provisions required by the GPL. |
| 38 | If you do not delete the provisions above, a recipient may use your |
| 39 | version of this file under either the OSL or the GPL. |
| 40 | </para> |
| 41 | |
| 42 | </legalnotice> |
| 43 | </bookinfo> |
| 44 | |
| 45 | <toc></toc> |
| 46 | |
Jeff Garzik | 07dd39b | 2005-05-30 13:15:52 -0400 | [diff] [blame] | 47 | <chapter id="libataIntroduction"> |
| 48 | <title>Introduction</title> |
| 49 | <para> |
| 50 | libATA is a library used inside the Linux kernel to support ATA host |
| 51 | controllers and devices. libATA provides an ATA driver API, class |
| 52 | transports for ATA and ATAPI devices, and SCSI<->ATA translation |
| 53 | for ATA devices according to the T10 SAT specification. |
| 54 | </para> |
| 55 | <para> |
| 56 | This Guide documents the libATA driver API, library functions, library |
| 57 | internals, and a couple sample ATA low-level drivers. |
| 58 | </para> |
| 59 | </chapter> |
| 60 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 61 | <chapter id="libataDriverApi"> |
| 62 | <title>libata Driver API</title> |
Jeff Garzik | 92bab26 | 2005-05-31 20:43:57 -0400 | [diff] [blame] | 63 | <para> |
| 64 | struct ata_port_operations is defined for every low-level libata |
| 65 | hardware driver, and it controls how the low-level driver |
| 66 | interfaces with the ATA and SCSI layers. |
| 67 | </para> |
| 68 | <para> |
| 69 | FIS-based drivers will hook into the system with ->qc_prep() and |
| 70 | ->qc_issue() high-level hooks. Hardware which behaves in a manner |
| 71 | similar to PCI IDE hardware may utilize several generic helpers, |
| 72 | defining at a bare minimum the bus I/O addresses of the ATA shadow |
| 73 | register blocks. |
| 74 | </para> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 75 | <sect1> |
| 76 | <title>struct ata_port_operations</title> |
| 77 | |
Jeff Garzik | 92bab26 | 2005-05-31 20:43:57 -0400 | [diff] [blame] | 78 | <sect2><title>Disable ATA port</title> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 79 | <programlisting> |
| 80 | void (*port_disable) (struct ata_port *); |
| 81 | </programlisting> |
| 82 | |
| 83 | <para> |
| 84 | Called from ata_bus_probe() and ata_bus_reset() error paths, |
| 85 | as well as when unregistering from the SCSI module (rmmod, hot |
| 86 | unplug). |
Edward Falk | 8b2af8f | 2005-06-15 14:26:39 -0700 | [diff] [blame] | 87 | This function should do whatever needs to be done to take the |
| 88 | port out of use. In most cases, ata_port_disable() can be used |
| 89 | as this hook. |
| 90 | </para> |
| 91 | <para> |
| 92 | Called from ata_bus_probe() on a failed probe. |
| 93 | Called from ata_bus_reset() on a failed bus reset. |
| 94 | Called from ata_scsi_release(). |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 95 | </para> |
| 96 | |
Jeff Garzik | 92bab26 | 2005-05-31 20:43:57 -0400 | [diff] [blame] | 97 | </sect2> |
| 98 | |
| 99 | <sect2><title>Post-IDENTIFY device configuration</title> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 100 | <programlisting> |
| 101 | void (*dev_config) (struct ata_port *, struct ata_device *); |
| 102 | </programlisting> |
| 103 | |
| 104 | <para> |
| 105 | Called after IDENTIFY [PACKET] DEVICE is issued to each device |
| 106 | found. Typically used to apply device-specific fixups prior to |
| 107 | issue of SET FEATURES - XFER MODE, and prior to operation. |
| 108 | </para> |
Edward Falk | 8b2af8f | 2005-06-15 14:26:39 -0700 | [diff] [blame] | 109 | <para> |
| 110 | Called by ata_device_add() after ata_dev_identify() determines |
| 111 | a device is present. |
| 112 | </para> |
| 113 | <para> |
| 114 | This entry may be specified as NULL in ata_port_operations. |
| 115 | </para> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 116 | |
Jeff Garzik | 92bab26 | 2005-05-31 20:43:57 -0400 | [diff] [blame] | 117 | </sect2> |
| 118 | |
| 119 | <sect2><title>Set PIO/DMA mode</title> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 120 | <programlisting> |
| 121 | void (*set_piomode) (struct ata_port *, struct ata_device *); |
| 122 | void (*set_dmamode) (struct ata_port *, struct ata_device *); |
Alan Cox | 5444a6f | 2006-03-27 18:58:20 +0100 | [diff] [blame] | 123 | void (*post_set_mode) (struct ata_port *); |
| 124 | unsigned int (*mode_filter) (struct ata_port *, struct ata_device *, unsigned int); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 125 | </programlisting> |
| 126 | |
| 127 | <para> |
| 128 | Hooks called prior to the issue of SET FEATURES - XFER MODE |
Alan Cox | 5444a6f | 2006-03-27 18:58:20 +0100 | [diff] [blame] | 129 | command. The optional ->mode_filter() hook is called when libata |
| 130 | has built a mask of the possible modes. This is passed to the |
| 131 | ->mode_filter() function which should return a mask of valid modes |
| 132 | after filtering those unsuitable due to hardware limits. It is not |
| 133 | valid to use this interface to add modes. |
| 134 | </para> |
| 135 | <para> |
| 136 | dev->pio_mode and dev->dma_mode are guaranteed to be valid when |
| 137 | ->set_piomode() and when ->set_dmamode() is called. The timings for |
| 138 | any other drive sharing the cable will also be valid at this point. |
| 139 | That is the library records the decisions for the modes of each |
| 140 | drive on a channel before it attempts to set any of them. |
| 141 | </para> |
| 142 | <para> |
| 143 | ->post_set_mode() is |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 144 | called unconditionally, after the SET FEATURES - XFER MODE |
| 145 | command completes successfully. |
| 146 | </para> |
| 147 | |
| 148 | <para> |
| 149 | ->set_piomode() is always called (if present), but |
| 150 | ->set_dma_mode() is only called if DMA is possible. |
| 151 | </para> |
| 152 | |
Jeff Garzik | 92bab26 | 2005-05-31 20:43:57 -0400 | [diff] [blame] | 153 | </sect2> |
| 154 | |
| 155 | <sect2><title>Taskfile read/write</title> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 156 | <programlisting> |
| 157 | void (*tf_load) (struct ata_port *ap, struct ata_taskfile *tf); |
| 158 | void (*tf_read) (struct ata_port *ap, struct ata_taskfile *tf); |
| 159 | </programlisting> |
| 160 | |
| 161 | <para> |
| 162 | ->tf_load() is called to load the given taskfile into hardware |
| 163 | registers / DMA buffers. ->tf_read() is called to read the |
| 164 | hardware registers / DMA buffers, to obtain the current set of |
| 165 | taskfile register values. |
Edward Falk | 8b2af8f | 2005-06-15 14:26:39 -0700 | [diff] [blame] | 166 | Most drivers for taskfile-based hardware (PIO or MMIO) use |
| 167 | ata_tf_load() and ata_tf_read() for these hooks. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 168 | </para> |
| 169 | |
Jeff Garzik | 92bab26 | 2005-05-31 20:43:57 -0400 | [diff] [blame] | 170 | </sect2> |
| 171 | |
Jeff Garzik | bf717b11 | 2006-06-13 20:27:03 -0400 | [diff] [blame] | 172 | <sect2><title>PIO data read/write</title> |
| 173 | <programlisting> |
| 174 | void (*data_xfer) (struct ata_device *, unsigned char *, unsigned int, int); |
| 175 | </programlisting> |
| 176 | |
| 177 | <para> |
| 178 | All bmdma-style drivers must implement this hook. This is the low-level |
| 179 | operation that actually copies the data bytes during a PIO data |
| 180 | transfer. |
| 181 | Typically the driver |
| 182 | will choose one of ata_pio_data_xfer_noirq(), ata_pio_data_xfer(), or |
| 183 | ata_mmio_data_xfer(). |
| 184 | </para> |
| 185 | |
| 186 | </sect2> |
| 187 | |
Jeff Garzik | 92bab26 | 2005-05-31 20:43:57 -0400 | [diff] [blame] | 188 | <sect2><title>ATA command execute</title> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 189 | <programlisting> |
| 190 | void (*exec_command)(struct ata_port *ap, struct ata_taskfile *tf); |
| 191 | </programlisting> |
| 192 | |
| 193 | <para> |
| 194 | causes an ATA command, previously loaded with |
| 195 | ->tf_load(), to be initiated in hardware. |
Edward Falk | 8b2af8f | 2005-06-15 14:26:39 -0700 | [diff] [blame] | 196 | Most drivers for taskfile-based hardware use ata_exec_command() |
| 197 | for this hook. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 198 | </para> |
| 199 | |
Jeff Garzik | 92bab26 | 2005-05-31 20:43:57 -0400 | [diff] [blame] | 200 | </sect2> |
| 201 | |
| 202 | <sect2><title>Per-cmd ATAPI DMA capabilities filter</title> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 203 | <programlisting> |
Jeff Garzik | 780a87f | 2005-05-30 15:41:05 -0400 | [diff] [blame] | 204 | int (*check_atapi_dma) (struct ata_queued_cmd *qc); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 205 | </programlisting> |
| 206 | |
| 207 | <para> |
Jeff Garzik | 780a87f | 2005-05-30 15:41:05 -0400 | [diff] [blame] | 208 | Allow low-level driver to filter ATA PACKET commands, returning a status |
| 209 | indicating whether or not it is OK to use DMA for the supplied PACKET |
| 210 | command. |
| 211 | </para> |
Edward Falk | 8b2af8f | 2005-06-15 14:26:39 -0700 | [diff] [blame] | 212 | <para> |
| 213 | This hook may be specified as NULL, in which case libata will |
| 214 | assume that atapi dma can be supported. |
| 215 | </para> |
Jeff Garzik | 780a87f | 2005-05-30 15:41:05 -0400 | [diff] [blame] | 216 | |
Jeff Garzik | 92bab26 | 2005-05-31 20:43:57 -0400 | [diff] [blame] | 217 | </sect2> |
| 218 | |
| 219 | <sect2><title>Read specific ATA shadow registers</title> |
Jeff Garzik | 780a87f | 2005-05-30 15:41:05 -0400 | [diff] [blame] | 220 | <programlisting> |
| 221 | u8 (*check_status)(struct ata_port *ap); |
| 222 | u8 (*check_altstatus)(struct ata_port *ap); |
Jeff Garzik | 780a87f | 2005-05-30 15:41:05 -0400 | [diff] [blame] | 223 | </programlisting> |
| 224 | |
| 225 | <para> |
Jeff Garzik | bf717b11 | 2006-06-13 20:27:03 -0400 | [diff] [blame] | 226 | Reads the Status/AltStatus ATA shadow register from |
Jeff Garzik | 780a87f | 2005-05-30 15:41:05 -0400 | [diff] [blame] | 227 | hardware. On some hardware, reading the Status register has |
| 228 | the side effect of clearing the interrupt condition. |
Edward Falk | 8b2af8f | 2005-06-15 14:26:39 -0700 | [diff] [blame] | 229 | Most drivers for taskfile-based hardware use |
| 230 | ata_check_status() for this hook. |
| 231 | </para> |
| 232 | <para> |
| 233 | Note that because this is called from ata_device_add(), at |
| 234 | least a dummy function that clears device interrupts must be |
| 235 | provided for all drivers, even if the controller doesn't |
| 236 | actually have a taskfile status register. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 237 | </para> |
| 238 | |
Jeff Garzik | 92bab26 | 2005-05-31 20:43:57 -0400 | [diff] [blame] | 239 | </sect2> |
| 240 | |
| 241 | <sect2><title>Select ATA device on bus</title> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 242 | <programlisting> |
| 243 | void (*dev_select)(struct ata_port *ap, unsigned int device); |
| 244 | </programlisting> |
| 245 | |
| 246 | <para> |
| 247 | Issues the low-level hardware command(s) that causes one of N |
| 248 | hardware devices to be considered 'selected' (active and |
Jeff Garzik | 780a87f | 2005-05-30 15:41:05 -0400 | [diff] [blame] | 249 | available for use) on the ATA bus. This generally has no |
Edward Falk | 8b2af8f | 2005-06-15 14:26:39 -0700 | [diff] [blame] | 250 | meaning on FIS-based devices. |
| 251 | </para> |
| 252 | <para> |
| 253 | Most drivers for taskfile-based hardware use |
| 254 | ata_std_dev_select() for this hook. Controllers which do not |
| 255 | support second drives on a port (such as SATA contollers) will |
| 256 | use ata_noop_dev_select(). |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 257 | </para> |
| 258 | |
Jeff Garzik | 92bab26 | 2005-05-31 20:43:57 -0400 | [diff] [blame] | 259 | </sect2> |
| 260 | |
Alan Cox | 5444a6f | 2006-03-27 18:58:20 +0100 | [diff] [blame] | 261 | <sect2><title>Private tuning method</title> |
| 262 | <programlisting> |
| 263 | void (*set_mode) (struct ata_port *ap); |
| 264 | </programlisting> |
| 265 | |
| 266 | <para> |
| 267 | By default libata performs drive and controller tuning in |
| 268 | accordance with the ATA timing rules and also applies blacklists |
| 269 | and cable limits. Some controllers need special handling and have |
| 270 | custom tuning rules, typically raid controllers that use ATA |
| 271 | commands but do not actually do drive timing. |
| 272 | </para> |
| 273 | |
| 274 | <warning> |
| 275 | <para> |
| 276 | This hook should not be used to replace the standard controller |
| 277 | tuning logic when a controller has quirks. Replacing the default |
| 278 | tuning logic in that case would bypass handling for drive and |
| 279 | bridge quirks that may be important to data reliability. If a |
| 280 | controller needs to filter the mode selection it should use the |
| 281 | mode_filter hook instead. |
| 282 | </para> |
| 283 | </warning> |
| 284 | |
| 285 | </sect2> |
| 286 | |
Jeff Garzik | 92bab26 | 2005-05-31 20:43:57 -0400 | [diff] [blame] | 287 | <sect2><title>Control PCI IDE BMDMA engine</title> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 288 | <programlisting> |
| 289 | void (*bmdma_setup) (struct ata_queued_cmd *qc); |
| 290 | void (*bmdma_start) (struct ata_queued_cmd *qc); |
Jeff Garzik | 780a87f | 2005-05-30 15:41:05 -0400 | [diff] [blame] | 291 | void (*bmdma_stop) (struct ata_port *ap); |
| 292 | u8 (*bmdma_status) (struct ata_port *ap); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 293 | </programlisting> |
| 294 | |
| 295 | <para> |
Jeff Garzik | 780a87f | 2005-05-30 15:41:05 -0400 | [diff] [blame] | 296 | When setting up an IDE BMDMA transaction, these hooks arm |
| 297 | (->bmdma_setup), fire (->bmdma_start), and halt (->bmdma_stop) |
| 298 | the hardware's DMA engine. ->bmdma_status is used to read the standard |
| 299 | PCI IDE DMA Status register. |
| 300 | </para> |
| 301 | |
| 302 | <para> |
| 303 | These hooks are typically either no-ops, or simply not implemented, in |
| 304 | FIS-based drivers. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 305 | </para> |
Edward Falk | 8b2af8f | 2005-06-15 14:26:39 -0700 | [diff] [blame] | 306 | <para> |
| 307 | Most legacy IDE drivers use ata_bmdma_setup() for the bmdma_setup() |
| 308 | hook. ata_bmdma_setup() will write the pointer to the PRD table to |
| 309 | the IDE PRD Table Address register, enable DMA in the DMA Command |
| 310 | register, and call exec_command() to begin the transfer. |
| 311 | </para> |
| 312 | <para> |
| 313 | Most legacy IDE drivers use ata_bmdma_start() for the bmdma_start() |
| 314 | hook. ata_bmdma_start() will write the ATA_DMA_START flag to the DMA |
| 315 | Command register. |
| 316 | </para> |
| 317 | <para> |
| 318 | Many legacy IDE drivers use ata_bmdma_stop() for the bmdma_stop() |
| 319 | hook. ata_bmdma_stop() clears the ATA_DMA_START flag in the DMA |
| 320 | command register. |
| 321 | </para> |
| 322 | <para> |
| 323 | Many legacy IDE drivers use ata_bmdma_status() as the bmdma_status() hook. |
| 324 | </para> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 325 | |
Jeff Garzik | 92bab26 | 2005-05-31 20:43:57 -0400 | [diff] [blame] | 326 | </sect2> |
| 327 | |
| 328 | <sect2><title>High-level taskfile hooks</title> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 329 | <programlisting> |
| 330 | void (*qc_prep) (struct ata_queued_cmd *qc); |
| 331 | int (*qc_issue) (struct ata_queued_cmd *qc); |
| 332 | </programlisting> |
| 333 | |
| 334 | <para> |
| 335 | Higher-level hooks, these two hooks can potentially supercede |
| 336 | several of the above taskfile/DMA engine hooks. ->qc_prep is |
| 337 | called after the buffers have been DMA-mapped, and is typically |
| 338 | used to populate the hardware's DMA scatter-gather table. |
| 339 | Most drivers use the standard ata_qc_prep() helper function, but |
| 340 | more advanced drivers roll their own. |
| 341 | </para> |
| 342 | <para> |
| 343 | ->qc_issue is used to make a command active, once the hardware |
| 344 | and S/G tables have been prepared. IDE BMDMA drivers use the |
| 345 | helper function ata_qc_issue_prot() for taskfile protocol-based |
Jeff Garzik | 780a87f | 2005-05-30 15:41:05 -0400 | [diff] [blame] | 346 | dispatch. More advanced drivers implement their own ->qc_issue. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 347 | </para> |
Edward Falk | 8b2af8f | 2005-06-15 14:26:39 -0700 | [diff] [blame] | 348 | <para> |
| 349 | ata_qc_issue_prot() calls ->tf_load(), ->bmdma_setup(), and |
| 350 | ->bmdma_start() as necessary to initiate a transfer. |
| 351 | </para> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 352 | |
Jeff Garzik | 92bab26 | 2005-05-31 20:43:57 -0400 | [diff] [blame] | 353 | </sect2> |
| 354 | |
Jeff Garzik | bf717b11 | 2006-06-13 20:27:03 -0400 | [diff] [blame] | 355 | <sect2><title>Exception and probe handling (EH)</title> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 356 | <programlisting> |
| 357 | void (*eng_timeout) (struct ata_port *ap); |
Jeff Garzik | bf717b11 | 2006-06-13 20:27:03 -0400 | [diff] [blame] | 358 | void (*phy_reset) (struct ata_port *ap); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 359 | </programlisting> |
| 360 | |
| 361 | <para> |
Jeff Garzik | bf717b11 | 2006-06-13 20:27:03 -0400 | [diff] [blame] | 362 | Deprecated. Use ->error_handler() instead. |
| 363 | </para> |
| 364 | |
| 365 | <programlisting> |
| 366 | void (*freeze) (struct ata_port *ap); |
| 367 | void (*thaw) (struct ata_port *ap); |
| 368 | </programlisting> |
| 369 | |
| 370 | <para> |
| 371 | ata_port_freeze() is called when HSM violations or some other |
| 372 | condition disrupts normal operation of the port. A frozen port |
| 373 | is not allowed to perform any operation until the port is |
| 374 | thawed, which usually follows a successful reset. |
| 375 | </para> |
| 376 | |
| 377 | <para> |
| 378 | The optional ->freeze() callback can be used for freezing the port |
| 379 | hardware-wise (e.g. mask interrupt and stop DMA engine). If a |
| 380 | port cannot be frozen hardware-wise, the interrupt handler |
| 381 | must ack and clear interrupts unconditionally while the port |
| 382 | is frozen. |
| 383 | </para> |
| 384 | <para> |
| 385 | The optional ->thaw() callback is called to perform the opposite of ->freeze(): |
| 386 | prepare the port for normal operation once again. Unmask interrupts, |
| 387 | start DMA engine, etc. |
| 388 | </para> |
| 389 | |
| 390 | <programlisting> |
| 391 | void (*error_handler) (struct ata_port *ap); |
| 392 | </programlisting> |
| 393 | |
| 394 | <para> |
| 395 | ->error_handler() is a driver's hook into probe, hotplug, and recovery |
| 396 | and other exceptional conditions. The primary responsibility of an |
| 397 | implementation is to call ata_do_eh() or ata_bmdma_drive_eh() with a set |
| 398 | of EH hooks as arguments: |
| 399 | </para> |
| 400 | |
| 401 | <para> |
| 402 | 'prereset' hook (may be NULL) is called during an EH reset, before any other actions |
| 403 | are taken. |
| 404 | </para> |
| 405 | |
| 406 | <para> |
| 407 | 'postreset' hook (may be NULL) is called after the EH reset is performed. Based on |
| 408 | existing conditions, severity of the problem, and hardware capabilities, |
| 409 | </para> |
| 410 | |
| 411 | <para> |
| 412 | Either 'softreset' (may be NULL) or 'hardreset' (may be NULL) will be |
| 413 | called to perform the low-level EH reset. |
| 414 | </para> |
| 415 | |
| 416 | <programlisting> |
| 417 | void (*post_internal_cmd) (struct ata_queued_cmd *qc); |
| 418 | </programlisting> |
| 419 | |
| 420 | <para> |
| 421 | Perform any hardware-specific actions necessary to finish processing |
| 422 | after executing a probe-time or EH-time command via ata_exec_internal(). |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 423 | </para> |
| 424 | |
Jeff Garzik | 92bab26 | 2005-05-31 20:43:57 -0400 | [diff] [blame] | 425 | </sect2> |
| 426 | |
| 427 | <sect2><title>Hardware interrupt handling</title> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 428 | <programlisting> |
| 429 | irqreturn_t (*irq_handler)(int, void *, struct pt_regs *); |
| 430 | void (*irq_clear) (struct ata_port *); |
| 431 | </programlisting> |
| 432 | |
| 433 | <para> |
| 434 | ->irq_handler is the interrupt handling routine registered with |
| 435 | the system, by libata. ->irq_clear is called during probe just |
| 436 | before the interrupt handler is registered, to be sure hardware |
| 437 | is quiet. |
| 438 | </para> |
Edward Falk | 8b2af8f | 2005-06-15 14:26:39 -0700 | [diff] [blame] | 439 | <para> |
| 440 | The second argument, dev_instance, should be cast to a pointer |
| 441 | to struct ata_host_set. |
| 442 | </para> |
| 443 | <para> |
| 444 | Most legacy IDE drivers use ata_interrupt() for the |
| 445 | irq_handler hook, which scans all ports in the host_set, |
| 446 | determines which queued command was active (if any), and calls |
| 447 | ata_host_intr(ap,qc). |
| 448 | </para> |
| 449 | <para> |
| 450 | Most legacy IDE drivers use ata_bmdma_irq_clear() for the |
| 451 | irq_clear() hook, which simply clears the interrupt and error |
| 452 | flags in the DMA status register. |
| 453 | </para> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 454 | |
Jeff Garzik | 92bab26 | 2005-05-31 20:43:57 -0400 | [diff] [blame] | 455 | </sect2> |
| 456 | |
| 457 | <sect2><title>SATA phy read/write</title> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 458 | <programlisting> |
| 459 | u32 (*scr_read) (struct ata_port *ap, unsigned int sc_reg); |
| 460 | void (*scr_write) (struct ata_port *ap, unsigned int sc_reg, |
| 461 | u32 val); |
| 462 | </programlisting> |
| 463 | |
| 464 | <para> |
| 465 | Read and write standard SATA phy registers. Currently only used |
| 466 | if ->phy_reset hook called the sata_phy_reset() helper function. |
Edward Falk | 8b2af8f | 2005-06-15 14:26:39 -0700 | [diff] [blame] | 467 | sc_reg is one of SCR_STATUS, SCR_CONTROL, SCR_ERROR, or SCR_ACTIVE. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 468 | </para> |
| 469 | |
Jeff Garzik | 92bab26 | 2005-05-31 20:43:57 -0400 | [diff] [blame] | 470 | </sect2> |
| 471 | |
| 472 | <sect2><title>Init and shutdown</title> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 473 | <programlisting> |
| 474 | int (*port_start) (struct ata_port *ap); |
| 475 | void (*port_stop) (struct ata_port *ap); |
| 476 | void (*host_stop) (struct ata_host_set *host_set); |
| 477 | </programlisting> |
| 478 | |
| 479 | <para> |
| 480 | ->port_start() is called just after the data structures for each |
| 481 | port are initialized. Typically this is used to alloc per-port |
| 482 | DMA buffers / tables / rings, enable DMA engines, and similar |
Edward Falk | 8b2af8f | 2005-06-15 14:26:39 -0700 | [diff] [blame] | 483 | tasks. Some drivers also use this entry point as a chance to |
| 484 | allocate driver-private memory for ap->private_data. |
| 485 | </para> |
| 486 | <para> |
| 487 | Many drivers use ata_port_start() as this hook or call |
| 488 | it from their own port_start() hooks. ata_port_start() |
| 489 | allocates space for a legacy IDE PRD table and returns. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 490 | </para> |
| 491 | <para> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 492 | ->port_stop() is called after ->host_stop(). It's sole function |
| 493 | is to release DMA/memory resources, now that they are no longer |
Edward Falk | 8b2af8f | 2005-06-15 14:26:39 -0700 | [diff] [blame] | 494 | actively being used. Many drivers also free driver-private |
| 495 | data from port at this time. |
| 496 | </para> |
| 497 | <para> |
| 498 | Many drivers use ata_port_stop() as this hook, which frees the |
| 499 | PRD table. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 500 | </para> |
Jeff Garzik | 780a87f | 2005-05-30 15:41:05 -0400 | [diff] [blame] | 501 | <para> |
| 502 | ->host_stop() is called after all ->port_stop() calls |
| 503 | have completed. The hook must finalize hardware shutdown, release DMA |
| 504 | and other resources, etc. |
Edward Falk | 8b2af8f | 2005-06-15 14:26:39 -0700 | [diff] [blame] | 505 | This hook may be specified as NULL, in which case it is not called. |
Jeff Garzik | 780a87f | 2005-05-30 15:41:05 -0400 | [diff] [blame] | 506 | </para> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 507 | |
Jeff Garzik | 92bab26 | 2005-05-31 20:43:57 -0400 | [diff] [blame] | 508 | </sect2> |
| 509 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 510 | </sect1> |
Jeff Garzik | a121349 | 2005-09-28 13:26:47 -0400 | [diff] [blame] | 511 | </chapter> |
| 512 | |
| 513 | <chapter id="libataEH"> |
Tejun Heo | bfd0072 | 2005-09-26 11:28:47 +0900 | [diff] [blame] | 514 | <title>Error handling</title> |
| 515 | |
| 516 | <para> |
| 517 | This chapter describes how errors are handled under libata. |
| 518 | Readers are advised to read SCSI EH |
| 519 | (Documentation/scsi/scsi_eh.txt) and ATA exceptions doc first. |
| 520 | </para> |
| 521 | |
Jeff Garzik | a121349 | 2005-09-28 13:26:47 -0400 | [diff] [blame] | 522 | <sect1><title>Origins of commands</title> |
Tejun Heo | bfd0072 | 2005-09-26 11:28:47 +0900 | [diff] [blame] | 523 | <para> |
| 524 | In libata, a command is represented with struct ata_queued_cmd |
| 525 | or qc. qc's are preallocated during port initialization and |
| 526 | repetitively used for command executions. Currently only one |
| 527 | qc is allocated per port but yet-to-be-merged NCQ branch |
| 528 | allocates one for each tag and maps each qc to NCQ tag 1-to-1. |
| 529 | </para> |
| 530 | <para> |
| 531 | libata commands can originate from two sources - libata itself |
| 532 | and SCSI midlayer. libata internal commands are used for |
| 533 | initialization and error handling. All normal blk requests |
| 534 | and commands for SCSI emulation are passed as SCSI commands |
| 535 | through queuecommand callback of SCSI host template. |
| 536 | </para> |
Jeff Garzik | a121349 | 2005-09-28 13:26:47 -0400 | [diff] [blame] | 537 | </sect1> |
Tejun Heo | bfd0072 | 2005-09-26 11:28:47 +0900 | [diff] [blame] | 538 | |
Jeff Garzik | a121349 | 2005-09-28 13:26:47 -0400 | [diff] [blame] | 539 | <sect1><title>How commands are issued</title> |
Tejun Heo | bfd0072 | 2005-09-26 11:28:47 +0900 | [diff] [blame] | 540 | |
| 541 | <variablelist> |
| 542 | |
| 543 | <varlistentry><term>Internal commands</term> |
| 544 | <listitem> |
| 545 | <para> |
| 546 | First, qc is allocated and initialized using |
| 547 | ata_qc_new_init(). Although ata_qc_new_init() doesn't |
| 548 | implement any wait or retry mechanism when qc is not |
| 549 | available, internal commands are currently issued only during |
| 550 | initialization and error recovery, so no other command is |
| 551 | active and allocation is guaranteed to succeed. |
| 552 | </para> |
| 553 | <para> |
| 554 | Once allocated qc's taskfile is initialized for the command to |
| 555 | be executed. qc currently has two mechanisms to notify |
| 556 | completion. One is via qc->complete_fn() callback and the |
| 557 | other is completion qc->waiting. qc->complete_fn() callback |
| 558 | is the asynchronous path used by normal SCSI translated |
| 559 | commands and qc->waiting is the synchronous (issuer sleeps in |
| 560 | process context) path used by internal commands. |
| 561 | </para> |
| 562 | <para> |
| 563 | Once initialization is complete, host_set lock is acquired |
| 564 | and the qc is issued. |
| 565 | </para> |
| 566 | </listitem> |
| 567 | </varlistentry> |
| 568 | |
| 569 | <varlistentry><term>SCSI commands</term> |
| 570 | <listitem> |
| 571 | <para> |
| 572 | All libata drivers use ata_scsi_queuecmd() as |
| 573 | hostt->queuecommand callback. scmds can either be simulated |
| 574 | or translated. No qc is involved in processing a simulated |
| 575 | scmd. The result is computed right away and the scmd is |
| 576 | completed. |
| 577 | </para> |
| 578 | <para> |
| 579 | For a translated scmd, ata_qc_new_init() is invoked to |
| 580 | allocate a qc and the scmd is translated into the qc. SCSI |
| 581 | midlayer's completion notification function pointer is stored |
| 582 | into qc->scsidone. |
| 583 | </para> |
| 584 | <para> |
| 585 | qc->complete_fn() callback is used for completion |
| 586 | notification. ATA commands use ata_scsi_qc_complete() while |
| 587 | ATAPI commands use atapi_qc_complete(). Both functions end up |
| 588 | calling qc->scsidone to notify upper layer when the qc is |
| 589 | finished. After translation is completed, the qc is issued |
| 590 | with ata_qc_issue(). |
| 591 | </para> |
| 592 | <para> |
| 593 | Note that SCSI midlayer invokes hostt->queuecommand while |
| 594 | holding host_set lock, so all above occur while holding |
| 595 | host_set lock. |
| 596 | </para> |
| 597 | </listitem> |
| 598 | </varlistentry> |
| 599 | |
| 600 | </variablelist> |
Jeff Garzik | a121349 | 2005-09-28 13:26:47 -0400 | [diff] [blame] | 601 | </sect1> |
Tejun Heo | bfd0072 | 2005-09-26 11:28:47 +0900 | [diff] [blame] | 602 | |
Jeff Garzik | a121349 | 2005-09-28 13:26:47 -0400 | [diff] [blame] | 603 | <sect1><title>How commands are processed</title> |
Tejun Heo | bfd0072 | 2005-09-26 11:28:47 +0900 | [diff] [blame] | 604 | <para> |
| 605 | Depending on which protocol and which controller are used, |
| 606 | commands are processed differently. For the purpose of |
| 607 | discussion, a controller which uses taskfile interface and all |
| 608 | standard callbacks is assumed. |
| 609 | </para> |
| 610 | <para> |
| 611 | Currently 6 ATA command protocols are used. They can be |
| 612 | sorted into the following four categories according to how |
| 613 | they are processed. |
| 614 | </para> |
| 615 | |
| 616 | <variablelist> |
| 617 | <varlistentry><term>ATA NO DATA or DMA</term> |
| 618 | <listitem> |
| 619 | <para> |
| 620 | ATA_PROT_NODATA and ATA_PROT_DMA fall into this category. |
| 621 | These types of commands don't require any software |
| 622 | intervention once issued. Device will raise interrupt on |
| 623 | completion. |
| 624 | </para> |
| 625 | </listitem> |
| 626 | </varlistentry> |
| 627 | |
| 628 | <varlistentry><term>ATA PIO</term> |
| 629 | <listitem> |
| 630 | <para> |
| 631 | ATA_PROT_PIO is in this category. libata currently |
| 632 | implements PIO with polling. ATA_NIEN bit is set to turn |
| 633 | off interrupt and pio_task on ata_wq performs polling and |
| 634 | IO. |
| 635 | </para> |
| 636 | </listitem> |
| 637 | </varlistentry> |
| 638 | |
| 639 | <varlistentry><term>ATAPI NODATA or DMA</term> |
| 640 | <listitem> |
| 641 | <para> |
| 642 | ATA_PROT_ATAPI_NODATA and ATA_PROT_ATAPI_DMA are in this |
| 643 | category. packet_task is used to poll BSY bit after |
| 644 | issuing PACKET command. Once BSY is turned off by the |
| 645 | device, packet_task transfers CDB and hands off processing |
| 646 | to interrupt handler. |
| 647 | </para> |
| 648 | </listitem> |
| 649 | </varlistentry> |
| 650 | |
| 651 | <varlistentry><term>ATAPI PIO</term> |
| 652 | <listitem> |
| 653 | <para> |
| 654 | ATA_PROT_ATAPI is in this category. ATA_NIEN bit is set |
| 655 | and, as in ATAPI NODATA or DMA, packet_task submits cdb. |
| 656 | However, after submitting cdb, further processing (data |
| 657 | transfer) is handed off to pio_task. |
| 658 | </para> |
| 659 | </listitem> |
| 660 | </varlistentry> |
| 661 | </variablelist> |
Jeff Garzik | a121349 | 2005-09-28 13:26:47 -0400 | [diff] [blame] | 662 | </sect1> |
Tejun Heo | bfd0072 | 2005-09-26 11:28:47 +0900 | [diff] [blame] | 663 | |
Jeff Garzik | a121349 | 2005-09-28 13:26:47 -0400 | [diff] [blame] | 664 | <sect1><title>How commands are completed</title> |
Tejun Heo | bfd0072 | 2005-09-26 11:28:47 +0900 | [diff] [blame] | 665 | <para> |
| 666 | Once issued, all qc's are either completed with |
| 667 | ata_qc_complete() or time out. For commands which are handled |
| 668 | by interrupts, ata_host_intr() invokes ata_qc_complete(), and, |
| 669 | for PIO tasks, pio_task invokes ata_qc_complete(). In error |
| 670 | cases, packet_task may also complete commands. |
| 671 | </para> |
| 672 | <para> |
| 673 | ata_qc_complete() does the following. |
| 674 | </para> |
| 675 | |
| 676 | <orderedlist> |
| 677 | |
| 678 | <listitem> |
| 679 | <para> |
| 680 | DMA memory is unmapped. |
| 681 | </para> |
| 682 | </listitem> |
| 683 | |
| 684 | <listitem> |
| 685 | <para> |
| 686 | ATA_QCFLAG_ACTIVE is clared from qc->flags. |
| 687 | </para> |
| 688 | </listitem> |
| 689 | |
| 690 | <listitem> |
| 691 | <para> |
| 692 | qc->complete_fn() callback is invoked. If the return value of |
| 693 | the callback is not zero. Completion is short circuited and |
| 694 | ata_qc_complete() returns. |
| 695 | </para> |
| 696 | </listitem> |
| 697 | |
| 698 | <listitem> |
| 699 | <para> |
| 700 | __ata_qc_complete() is called, which does |
| 701 | <orderedlist> |
| 702 | |
| 703 | <listitem> |
| 704 | <para> |
| 705 | qc->flags is cleared to zero. |
| 706 | </para> |
| 707 | </listitem> |
| 708 | |
| 709 | <listitem> |
| 710 | <para> |
| 711 | ap->active_tag and qc->tag are poisoned. |
| 712 | </para> |
| 713 | </listitem> |
| 714 | |
| 715 | <listitem> |
| 716 | <para> |
| 717 | qc->waiting is claread & completed (in that order). |
| 718 | </para> |
| 719 | </listitem> |
| 720 | |
| 721 | <listitem> |
| 722 | <para> |
| 723 | qc is deallocated by clearing appropriate bit in ap->qactive. |
| 724 | </para> |
| 725 | </listitem> |
| 726 | |
| 727 | </orderedlist> |
| 728 | </para> |
| 729 | </listitem> |
| 730 | |
| 731 | </orderedlist> |
| 732 | |
| 733 | <para> |
| 734 | So, it basically notifies upper layer and deallocates qc. One |
| 735 | exception is short-circuit path in #3 which is used by |
| 736 | atapi_qc_complete(). |
| 737 | </para> |
| 738 | <para> |
| 739 | For all non-ATAPI commands, whether it fails or not, almost |
| 740 | the same code path is taken and very little error handling |
| 741 | takes place. A qc is completed with success status if it |
| 742 | succeeded, with failed status otherwise. |
| 743 | </para> |
| 744 | <para> |
| 745 | However, failed ATAPI commands require more handling as |
| 746 | REQUEST SENSE is needed to acquire sense data. If an ATAPI |
| 747 | command fails, ata_qc_complete() is invoked with error status, |
| 748 | which in turn invokes atapi_qc_complete() via |
| 749 | qc->complete_fn() callback. |
| 750 | </para> |
| 751 | <para> |
| 752 | This makes atapi_qc_complete() set scmd->result to |
| 753 | SAM_STAT_CHECK_CONDITION, complete the scmd and return 1. As |
| 754 | the sense data is empty but scmd->result is CHECK CONDITION, |
| 755 | SCSI midlayer will invoke EH for the scmd, and returning 1 |
| 756 | makes ata_qc_complete() to return without deallocating the qc. |
| 757 | This leads us to ata_scsi_error() with partially completed qc. |
| 758 | </para> |
| 759 | |
Jeff Garzik | a121349 | 2005-09-28 13:26:47 -0400 | [diff] [blame] | 760 | </sect1> |
Tejun Heo | bfd0072 | 2005-09-26 11:28:47 +0900 | [diff] [blame] | 761 | |
Jeff Garzik | a121349 | 2005-09-28 13:26:47 -0400 | [diff] [blame] | 762 | <sect1><title>ata_scsi_error()</title> |
Tejun Heo | bfd0072 | 2005-09-26 11:28:47 +0900 | [diff] [blame] | 763 | <para> |
Christoph Hellwig | 9227c33 | 2006-04-01 19:21:04 +0200 | [diff] [blame] | 764 | ata_scsi_error() is the current transportt->eh_strategy_handler() |
Tejun Heo | bfd0072 | 2005-09-26 11:28:47 +0900 | [diff] [blame] | 765 | for libata. As discussed above, this will be entered in two |
| 766 | cases - timeout and ATAPI error completion. This function |
| 767 | calls low level libata driver's eng_timeout() callback, the |
| 768 | standard callback for which is ata_eng_timeout(). It checks |
| 769 | if a qc is active and calls ata_qc_timeout() on the qc if so. |
| 770 | Actual error handling occurs in ata_qc_timeout(). |
| 771 | </para> |
| 772 | <para> |
| 773 | If EH is invoked for timeout, ata_qc_timeout() stops BMDMA and |
| 774 | completes the qc. Note that as we're currently in EH, we |
| 775 | cannot call scsi_done. As described in SCSI EH doc, a |
| 776 | recovered scmd should be either retried with |
| 777 | scsi_queue_insert() or finished with scsi_finish_command(). |
| 778 | Here, we override qc->scsidone with scsi_finish_command() and |
| 779 | calls ata_qc_complete(). |
| 780 | </para> |
| 781 | <para> |
| 782 | If EH is invoked due to a failed ATAPI qc, the qc here is |
| 783 | completed but not deallocated. The purpose of this |
| 784 | half-completion is to use the qc as place holder to make EH |
| 785 | code reach this place. This is a bit hackish, but it works. |
| 786 | </para> |
| 787 | <para> |
| 788 | Once control reaches here, the qc is deallocated by invoking |
| 789 | __ata_qc_complete() explicitly. Then, internal qc for REQUEST |
| 790 | SENSE is issued. Once sense data is acquired, scmd is |
| 791 | finished by directly invoking scsi_finish_command() on the |
| 792 | scmd. Note that as we already have completed and deallocated |
| 793 | the qc which was associated with the scmd, we don't need |
| 794 | to/cannot call ata_qc_complete() again. |
| 795 | </para> |
| 796 | |
Jeff Garzik | a121349 | 2005-09-28 13:26:47 -0400 | [diff] [blame] | 797 | </sect1> |
Tejun Heo | bfd0072 | 2005-09-26 11:28:47 +0900 | [diff] [blame] | 798 | |
Jeff Garzik | a121349 | 2005-09-28 13:26:47 -0400 | [diff] [blame] | 799 | <sect1><title>Problems with the current EH</title> |
Tejun Heo | bfd0072 | 2005-09-26 11:28:47 +0900 | [diff] [blame] | 800 | |
| 801 | <itemizedlist> |
| 802 | |
| 803 | <listitem> |
| 804 | <para> |
| 805 | Error representation is too crude. Currently any and all |
| 806 | error conditions are represented with ATA STATUS and ERROR |
| 807 | registers. Errors which aren't ATA device errors are treated |
| 808 | as ATA device errors by setting ATA_ERR bit. Better error |
| 809 | descriptor which can properly represent ATA and other |
| 810 | errors/exceptions is needed. |
| 811 | </para> |
| 812 | </listitem> |
| 813 | |
| 814 | <listitem> |
| 815 | <para> |
| 816 | When handling timeouts, no action is taken to make device |
| 817 | forget about the timed out command and ready for new commands. |
| 818 | </para> |
| 819 | </listitem> |
| 820 | |
| 821 | <listitem> |
| 822 | <para> |
| 823 | EH handling via ata_scsi_error() is not properly protected |
| 824 | from usual command processing. On EH entrance, the device is |
| 825 | not in quiescent state. Timed out commands may succeed or |
| 826 | fail any time. pio_task and atapi_task may still be running. |
| 827 | </para> |
| 828 | </listitem> |
| 829 | |
| 830 | <listitem> |
| 831 | <para> |
| 832 | Too weak error recovery. Devices / controllers causing HSM |
| 833 | mismatch errors and other errors quite often require reset to |
| 834 | return to known state. Also, advanced error handling is |
| 835 | necessary to support features like NCQ and hotplug. |
| 836 | </para> |
| 837 | </listitem> |
| 838 | |
| 839 | <listitem> |
| 840 | <para> |
| 841 | ATA errors are directly handled in the interrupt handler and |
| 842 | PIO errors in pio_task. This is problematic for advanced |
| 843 | error handling for the following reasons. |
| 844 | </para> |
| 845 | <para> |
| 846 | First, advanced error handling often requires context and |
| 847 | internal qc execution. |
| 848 | </para> |
| 849 | <para> |
| 850 | Second, even a simple failure (say, CRC error) needs |
| 851 | information gathering and could trigger complex error handling |
| 852 | (say, resetting & reconfiguring). Having multiple code |
| 853 | paths to gather information, enter EH and trigger actions |
| 854 | makes life painful. |
| 855 | </para> |
| 856 | <para> |
| 857 | Third, scattered EH code makes implementing low level drivers |
| 858 | difficult. Low level drivers override libata callbacks. If |
| 859 | EH is scattered over several places, each affected callbacks |
| 860 | should perform its part of error handling. This can be error |
| 861 | prone and painful. |
| 862 | </para> |
| 863 | </listitem> |
| 864 | |
| 865 | </itemizedlist> |
Jeff Garzik | a121349 | 2005-09-28 13:26:47 -0400 | [diff] [blame] | 866 | </sect1> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 867 | </chapter> |
| 868 | |
| 869 | <chapter id="libataExt"> |
| 870 | <title>libata Library</title> |
Henrik Kretzschmar | 58707cc | 2006-08-21 18:39:26 -0700 | [diff] [blame] | 871 | !Edrivers/ata/libata-core.c |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 872 | </chapter> |
| 873 | |
| 874 | <chapter id="libataInt"> |
| 875 | <title>libata Core Internals</title> |
Henrik Kretzschmar | 58707cc | 2006-08-21 18:39:26 -0700 | [diff] [blame] | 876 | !Idrivers/ata/libata-core.c |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 877 | </chapter> |
| 878 | |
| 879 | <chapter id="libataScsiInt"> |
| 880 | <title>libata SCSI translation/emulation</title> |
Henrik Kretzschmar | 58707cc | 2006-08-21 18:39:26 -0700 | [diff] [blame] | 881 | !Edrivers/ata/libata-scsi.c |
| 882 | !Idrivers/ata/libata-scsi.c |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 883 | </chapter> |
| 884 | |
Tejun Heo | fe998aa | 2005-10-02 11:54:29 +0900 | [diff] [blame] | 885 | <chapter id="ataExceptions"> |
| 886 | <title>ATA errors & exceptions</title> |
| 887 | |
| 888 | <para> |
| 889 | This chapter tries to identify what error/exception conditions exist |
| 890 | for ATA/ATAPI devices and describe how they should be handled in |
| 891 | implementation-neutral way. |
| 892 | </para> |
| 893 | |
| 894 | <para> |
| 895 | The term 'error' is used to describe conditions where either an |
| 896 | explicit error condition is reported from device or a command has |
| 897 | timed out. |
| 898 | </para> |
| 899 | |
| 900 | <para> |
| 901 | The term 'exception' is either used to describe exceptional |
| 902 | conditions which are not errors (say, power or hotplug events), or |
| 903 | to describe both errors and non-error exceptional conditions. Where |
| 904 | explicit distinction between error and exception is necessary, the |
| 905 | term 'non-error exception' is used. |
| 906 | </para> |
| 907 | |
| 908 | <sect1 id="excat"> |
| 909 | <title>Exception categories</title> |
| 910 | <para> |
| 911 | Exceptions are described primarily with respect to legacy |
| 912 | taskfile + bus master IDE interface. If a controller provides |
| 913 | other better mechanism for error reporting, mapping those into |
| 914 | categories described below shouldn't be difficult. |
| 915 | </para> |
| 916 | |
| 917 | <para> |
| 918 | In the following sections, two recovery actions - reset and |
| 919 | reconfiguring transport - are mentioned. These are described |
| 920 | further in <xref linkend="exrec"/>. |
| 921 | </para> |
| 922 | |
| 923 | <sect2 id="excatHSMviolation"> |
| 924 | <title>HSM violation</title> |
| 925 | <para> |
| 926 | This error is indicated when STATUS value doesn't match HSM |
| 927 | requirement during issuing or excution any ATA/ATAPI command. |
| 928 | </para> |
| 929 | |
| 930 | <itemizedlist> |
| 931 | <title>Examples</title> |
| 932 | |
| 933 | <listitem> |
| 934 | <para> |
| 935 | ATA_STATUS doesn't contain !BSY && DRDY && !DRQ while trying |
| 936 | to issue a command. |
| 937 | </para> |
| 938 | </listitem> |
| 939 | |
| 940 | <listitem> |
| 941 | <para> |
| 942 | !BSY && !DRQ during PIO data transfer. |
| 943 | </para> |
| 944 | </listitem> |
| 945 | |
| 946 | <listitem> |
| 947 | <para> |
| 948 | DRQ on command completion. |
| 949 | </para> |
| 950 | </listitem> |
| 951 | |
| 952 | <listitem> |
| 953 | <para> |
| 954 | !BSY && ERR after CDB tranfer starts but before the |
| 955 | last byte of CDB is transferred. ATA/ATAPI standard states |
| 956 | that "The device shall not terminate the PACKET command |
| 957 | with an error before the last byte of the command packet has |
| 958 | been written" in the error outputs description of PACKET |
| 959 | command and the state diagram doesn't include such |
| 960 | transitions. |
| 961 | </para> |
| 962 | </listitem> |
| 963 | |
| 964 | </itemizedlist> |
| 965 | |
| 966 | <para> |
| 967 | In these cases, HSM is violated and not much information |
| 968 | regarding the error can be acquired from STATUS or ERROR |
| 969 | register. IOW, this error can be anything - driver bug, |
| 970 | faulty device, controller and/or cable. |
| 971 | </para> |
| 972 | |
| 973 | <para> |
| 974 | As HSM is violated, reset is necessary to restore known state. |
| 975 | Reconfiguring transport for lower speed might be helpful too |
| 976 | as transmission errors sometimes cause this kind of errors. |
| 977 | </para> |
| 978 | </sect2> |
| 979 | |
| 980 | <sect2 id="excatDevErr"> |
| 981 | <title>ATA/ATAPI device error (non-NCQ / non-CHECK CONDITION)</title> |
| 982 | |
| 983 | <para> |
| 984 | These are errors detected and reported by ATA/ATAPI devices |
| 985 | indicating device problems. For this type of errors, STATUS |
| 986 | and ERROR register values are valid and describe error |
| 987 | condition. Note that some of ATA bus errors are detected by |
| 988 | ATA/ATAPI devices and reported using the same mechanism as |
| 989 | device errors. Those cases are described later in this |
| 990 | section. |
| 991 | </para> |
| 992 | |
| 993 | <para> |
| 994 | For ATA commands, this type of errors are indicated by !BSY |
| 995 | && ERR during command execution and on completion. |
| 996 | </para> |
| 997 | |
| 998 | <para>For ATAPI commands,</para> |
| 999 | |
| 1000 | <itemizedlist> |
| 1001 | |
| 1002 | <listitem> |
| 1003 | <para> |
| 1004 | !BSY && ERR && ABRT right after issuing PACKET |
| 1005 | indicates that PACKET command is not supported and falls in |
| 1006 | this category. |
| 1007 | </para> |
| 1008 | </listitem> |
| 1009 | |
| 1010 | <listitem> |
| 1011 | <para> |
| 1012 | !BSY && ERR(==CHK) && !ABRT after the last |
| 1013 | byte of CDB is transferred indicates CHECK CONDITION and |
| 1014 | doesn't fall in this category. |
| 1015 | </para> |
| 1016 | </listitem> |
| 1017 | |
| 1018 | <listitem> |
| 1019 | <para> |
| 1020 | !BSY && ERR(==CHK) && ABRT after the last byte |
| 1021 | of CDB is transferred *probably* indicates CHECK CONDITION and |
| 1022 | doesn't fall in this category. |
| 1023 | </para> |
| 1024 | </listitem> |
| 1025 | |
| 1026 | </itemizedlist> |
| 1027 | |
| 1028 | <para> |
| 1029 | Of errors detected as above, the followings are not ATA/ATAPI |
| 1030 | device errors but ATA bus errors and should be handled |
| 1031 | according to <xref linkend="excatATAbusErr"/>. |
| 1032 | </para> |
| 1033 | |
| 1034 | <variablelist> |
| 1035 | |
| 1036 | <varlistentry> |
| 1037 | <term>CRC error during data transfer</term> |
| 1038 | <listitem> |
| 1039 | <para> |
| 1040 | This is indicated by ICRC bit in the ERROR register and |
| 1041 | means that corruption occurred during data transfer. Upto |
| 1042 | ATA/ATAPI-7, the standard specifies that this bit is only |
| 1043 | applicable to UDMA transfers but ATA/ATAPI-8 draft revision |
| 1044 | 1f says that the bit may be applicable to multiword DMA and |
| 1045 | PIO. |
| 1046 | </para> |
| 1047 | </listitem> |
| 1048 | </varlistentry> |
| 1049 | |
| 1050 | <varlistentry> |
| 1051 | <term>ABRT error during data transfer or on completion</term> |
| 1052 | <listitem> |
| 1053 | <para> |
| 1054 | Upto ATA/ATAPI-7, the standard specifies that ABRT could be |
| 1055 | set on ICRC errors and on cases where a device is not able |
| 1056 | to complete a command. Combined with the fact that MWDMA |
| 1057 | and PIO transfer errors aren't allowed to use ICRC bit upto |
| 1058 | ATA/ATAPI-7, it seems to imply that ABRT bit alone could |
| 1059 | indicate tranfer errors. |
| 1060 | </para> |
| 1061 | <para> |
| 1062 | However, ATA/ATAPI-8 draft revision 1f removes the part |
| 1063 | that ICRC errors can turn on ABRT. So, this is kind of |
| 1064 | gray area. Some heuristics are needed here. |
| 1065 | </para> |
| 1066 | </listitem> |
| 1067 | </varlistentry> |
| 1068 | |
| 1069 | </variablelist> |
| 1070 | |
| 1071 | <para> |
| 1072 | ATA/ATAPI device errors can be further categorized as follows. |
| 1073 | </para> |
| 1074 | |
| 1075 | <variablelist> |
| 1076 | |
| 1077 | <varlistentry> |
| 1078 | <term>Media errors</term> |
| 1079 | <listitem> |
| 1080 | <para> |
| 1081 | This is indicated by UNC bit in the ERROR register. ATA |
| 1082 | devices reports UNC error only after certain number of |
| 1083 | retries cannot recover the data, so there's nothing much |
| 1084 | else to do other than notifying upper layer. |
| 1085 | </para> |
| 1086 | <para> |
| 1087 | READ and WRITE commands report CHS or LBA of the first |
| 1088 | failed sector but ATA/ATAPI standard specifies that the |
| 1089 | amount of transferred data on error completion is |
| 1090 | indeterminate, so we cannot assume that sectors preceding |
| 1091 | the failed sector have been transferred and thus cannot |
| 1092 | complete those sectors successfully as SCSI does. |
| 1093 | </para> |
| 1094 | </listitem> |
| 1095 | </varlistentry> |
| 1096 | |
| 1097 | <varlistentry> |
| 1098 | <term>Media changed / media change requested error</term> |
| 1099 | <listitem> |
| 1100 | <para> |
| 1101 | <<TODO: fill here>> |
| 1102 | </para> |
| 1103 | </listitem> |
| 1104 | </varlistentry> |
| 1105 | |
| 1106 | <varlistentry><term>Address error</term> |
| 1107 | <listitem> |
| 1108 | <para> |
| 1109 | This is indicated by IDNF bit in the ERROR register. |
| 1110 | Report to upper layer. |
| 1111 | </para> |
| 1112 | </listitem> |
| 1113 | </varlistentry> |
| 1114 | |
| 1115 | <varlistentry><term>Other errors</term> |
| 1116 | <listitem> |
| 1117 | <para> |
| 1118 | This can be invalid command or parameter indicated by ABRT |
| 1119 | ERROR bit or some other error condition. Note that ABRT |
| 1120 | bit can indicate a lot of things including ICRC and Address |
| 1121 | errors. Heuristics needed. |
| 1122 | </para> |
| 1123 | </listitem> |
| 1124 | </varlistentry> |
| 1125 | |
| 1126 | </variablelist> |
| 1127 | |
| 1128 | <para> |
| 1129 | Depending on commands, not all STATUS/ERROR bits are |
| 1130 | applicable. These non-applicable bits are marked with |
| 1131 | "na" in the output descriptions but upto ATA/ATAPI-7 |
| 1132 | no definition of "na" can be found. However, |
| 1133 | ATA/ATAPI-8 draft revision 1f describes "N/A" as |
| 1134 | follows. |
| 1135 | </para> |
| 1136 | |
| 1137 | <blockquote> |
| 1138 | <variablelist> |
| 1139 | <varlistentry><term>3.2.3.3a N/A</term> |
| 1140 | <listitem> |
| 1141 | <para> |
| 1142 | A keyword the indicates a field has no defined value in |
| 1143 | this standard and should not be checked by the host or |
| 1144 | device. N/A fields should be cleared to zero. |
| 1145 | </para> |
| 1146 | </listitem> |
| 1147 | </varlistentry> |
| 1148 | </variablelist> |
| 1149 | </blockquote> |
| 1150 | |
| 1151 | <para> |
| 1152 | So, it seems reasonable to assume that "na" bits are |
| 1153 | cleared to zero by devices and thus need no explicit masking. |
| 1154 | </para> |
| 1155 | |
| 1156 | </sect2> |
| 1157 | |
| 1158 | <sect2 id="excatATAPIcc"> |
| 1159 | <title>ATAPI device CHECK CONDITION</title> |
| 1160 | |
| 1161 | <para> |
| 1162 | ATAPI device CHECK CONDITION error is indicated by set CHK bit |
| 1163 | (ERR bit) in the STATUS register after the last byte of CDB is |
| 1164 | transferred for a PACKET command. For this kind of errors, |
| 1165 | sense data should be acquired to gather information regarding |
| 1166 | the errors. REQUEST SENSE packet command should be used to |
| 1167 | acquire sense data. |
| 1168 | </para> |
| 1169 | |
| 1170 | <para> |
| 1171 | Once sense data is acquired, this type of errors can be |
| 1172 | handled similary to other SCSI errors. Note that sense data |
| 1173 | may indicate ATA bus error (e.g. Sense Key 04h HARDWARE ERROR |
| 1174 | && ASC/ASCQ 47h/00h SCSI PARITY ERROR). In such |
| 1175 | cases, the error should be considered as an ATA bus error and |
| 1176 | handled according to <xref linkend="excatATAbusErr"/>. |
| 1177 | </para> |
| 1178 | |
| 1179 | </sect2> |
| 1180 | |
| 1181 | <sect2 id="excatNCQerr"> |
| 1182 | <title>ATA device error (NCQ)</title> |
| 1183 | |
| 1184 | <para> |
| 1185 | NCQ command error is indicated by cleared BSY and set ERR bit |
| 1186 | during NCQ command phase (one or more NCQ commands |
| 1187 | outstanding). Although STATUS and ERROR registers will |
| 1188 | contain valid values describing the error, READ LOG EXT is |
| 1189 | required to clear the error condition, determine which command |
| 1190 | has failed and acquire more information. |
| 1191 | </para> |
| 1192 | |
| 1193 | <para> |
| 1194 | READ LOG EXT Log Page 10h reports which tag has failed and |
| 1195 | taskfile register values describing the error. With this |
| 1196 | information the failed command can be handled as a normal ATA |
| 1197 | command error as in <xref linkend="excatDevErr"/> and all |
| 1198 | other in-flight commands must be retried. Note that this |
| 1199 | retry should not be counted - it's likely that commands |
| 1200 | retried this way would have completed normally if it were not |
| 1201 | for the failed command. |
| 1202 | </para> |
| 1203 | |
| 1204 | <para> |
| 1205 | Note that ATA bus errors can be reported as ATA device NCQ |
| 1206 | errors. This should be handled as described in <xref |
| 1207 | linkend="excatATAbusErr"/>. |
| 1208 | </para> |
| 1209 | |
| 1210 | <para> |
| 1211 | If READ LOG EXT Log Page 10h fails or reports NQ, we're |
| 1212 | thoroughly screwed. This condition should be treated |
| 1213 | according to <xref linkend="excatHSMviolation"/>. |
| 1214 | </para> |
| 1215 | |
| 1216 | </sect2> |
| 1217 | |
| 1218 | <sect2 id="excatATAbusErr"> |
| 1219 | <title>ATA bus error</title> |
| 1220 | |
| 1221 | <para> |
| 1222 | ATA bus error means that data corruption occurred during |
| 1223 | transmission over ATA bus (SATA or PATA). This type of errors |
| 1224 | can be indicated by |
| 1225 | </para> |
| 1226 | |
| 1227 | <itemizedlist> |
| 1228 | |
| 1229 | <listitem> |
| 1230 | <para> |
| 1231 | ICRC or ABRT error as described in <xref linkend="excatDevErr"/>. |
| 1232 | </para> |
| 1233 | </listitem> |
| 1234 | |
| 1235 | <listitem> |
| 1236 | <para> |
| 1237 | Controller-specific error completion with error information |
| 1238 | indicating transmission error. |
| 1239 | </para> |
| 1240 | </listitem> |
| 1241 | |
| 1242 | <listitem> |
| 1243 | <para> |
| 1244 | On some controllers, command timeout. In this case, there may |
| 1245 | be a mechanism to determine that the timeout is due to |
| 1246 | transmission error. |
| 1247 | </para> |
| 1248 | </listitem> |
| 1249 | |
| 1250 | <listitem> |
| 1251 | <para> |
| 1252 | Unknown/random errors, timeouts and all sorts of weirdities. |
| 1253 | </para> |
| 1254 | </listitem> |
| 1255 | |
| 1256 | </itemizedlist> |
| 1257 | |
| 1258 | <para> |
| 1259 | As described above, transmission errors can cause wide variety |
| 1260 | of symptoms ranging from device ICRC error to random device |
| 1261 | lockup, and, for many cases, there is no way to tell if an |
| 1262 | error condition is due to transmission error or not; |
| 1263 | therefore, it's necessary to employ some kind of heuristic |
| 1264 | when dealing with errors and timeouts. For example, |
| 1265 | encountering repetitive ABRT errors for known supported |
| 1266 | command is likely to indicate ATA bus error. |
| 1267 | </para> |
| 1268 | |
| 1269 | <para> |
| 1270 | Once it's determined that ATA bus errors have possibly |
| 1271 | occurred, lowering ATA bus transmission speed is one of |
| 1272 | actions which may alleviate the problem. See <xref |
| 1273 | linkend="exrecReconf"/> for more information. |
| 1274 | </para> |
| 1275 | |
| 1276 | </sect2> |
| 1277 | |
| 1278 | <sect2 id="excatPCIbusErr"> |
| 1279 | <title>PCI bus error</title> |
| 1280 | |
| 1281 | <para> |
| 1282 | Data corruption or other failures during transmission over PCI |
| 1283 | (or other system bus). For standard BMDMA, this is indicated |
| 1284 | by Error bit in the BMDMA Status register. This type of |
| 1285 | errors must be logged as it indicates something is very wrong |
| 1286 | with the system. Resetting host controller is recommended. |
| 1287 | </para> |
| 1288 | |
| 1289 | </sect2> |
| 1290 | |
| 1291 | <sect2 id="excatLateCompletion"> |
| 1292 | <title>Late completion</title> |
| 1293 | |
| 1294 | <para> |
| 1295 | This occurs when timeout occurs and the timeout handler finds |
| 1296 | out that the timed out command has completed successfully or |
| 1297 | with error. This is usually caused by lost interrupts. This |
| 1298 | type of errors must be logged. Resetting host controller is |
| 1299 | recommended. |
| 1300 | </para> |
| 1301 | |
| 1302 | </sect2> |
| 1303 | |
| 1304 | <sect2 id="excatUnknown"> |
| 1305 | <title>Unknown error (timeout)</title> |
| 1306 | |
| 1307 | <para> |
| 1308 | This is when timeout occurs and the command is still |
| 1309 | processing or the host and device are in unknown state. When |
| 1310 | this occurs, HSM could be in any valid or invalid state. To |
| 1311 | bring the device to known state and make it forget about the |
| 1312 | timed out command, resetting is necessary. The timed out |
| 1313 | command may be retried. |
| 1314 | </para> |
| 1315 | |
| 1316 | <para> |
| 1317 | Timeouts can also be caused by transmission errors. Refer to |
| 1318 | <xref linkend="excatATAbusErr"/> for more details. |
| 1319 | </para> |
| 1320 | |
| 1321 | </sect2> |
| 1322 | |
| 1323 | <sect2 id="excatHoplugPM"> |
| 1324 | <title>Hotplug and power management exceptions</title> |
| 1325 | |
| 1326 | <para> |
| 1327 | <<TODO: fill here>> |
| 1328 | </para> |
| 1329 | |
| 1330 | </sect2> |
| 1331 | |
| 1332 | </sect1> |
| 1333 | |
| 1334 | <sect1 id="exrec"> |
| 1335 | <title>EH recovery actions</title> |
| 1336 | |
| 1337 | <para> |
| 1338 | This section discusses several important recovery actions. |
| 1339 | </para> |
| 1340 | |
| 1341 | <sect2 id="exrecClr"> |
| 1342 | <title>Clearing error condition</title> |
| 1343 | |
| 1344 | <para> |
| 1345 | Many controllers require its error registers to be cleared by |
| 1346 | error handler. Different controllers may have different |
| 1347 | requirements. |
| 1348 | </para> |
| 1349 | |
| 1350 | <para> |
| 1351 | For SATA, it's strongly recommended to clear at least SError |
| 1352 | register during error handling. |
| 1353 | </para> |
| 1354 | </sect2> |
| 1355 | |
| 1356 | <sect2 id="exrecRst"> |
| 1357 | <title>Reset</title> |
| 1358 | |
| 1359 | <para> |
| 1360 | During EH, resetting is necessary in the following cases. |
| 1361 | </para> |
| 1362 | |
| 1363 | <itemizedlist> |
| 1364 | |
| 1365 | <listitem> |
| 1366 | <para> |
| 1367 | HSM is in unknown or invalid state |
| 1368 | </para> |
| 1369 | </listitem> |
| 1370 | |
| 1371 | <listitem> |
| 1372 | <para> |
| 1373 | HBA is in unknown or invalid state |
| 1374 | </para> |
| 1375 | </listitem> |
| 1376 | |
| 1377 | <listitem> |
| 1378 | <para> |
| 1379 | EH needs to make HBA/device forget about in-flight commands |
| 1380 | </para> |
| 1381 | </listitem> |
| 1382 | |
| 1383 | <listitem> |
| 1384 | <para> |
| 1385 | HBA/device behaves weirdly |
| 1386 | </para> |
| 1387 | </listitem> |
| 1388 | |
| 1389 | </itemizedlist> |
| 1390 | |
| 1391 | <para> |
| 1392 | Resetting during EH might be a good idea regardless of error |
| 1393 | condition to improve EH robustness. Whether to reset both or |
| 1394 | either one of HBA and device depends on situation but the |
| 1395 | following scheme is recommended. |
| 1396 | </para> |
| 1397 | |
| 1398 | <itemizedlist> |
| 1399 | |
| 1400 | <listitem> |
| 1401 | <para> |
| 1402 | When it's known that HBA is in ready state but ATA/ATAPI |
Paolo Ornati | 670e9f3 | 2006-10-03 22:57:56 +0200 | [diff] [blame] | 1403 | device is in unknown state, reset only device. |
Tejun Heo | fe998aa | 2005-10-02 11:54:29 +0900 | [diff] [blame] | 1404 | </para> |
| 1405 | </listitem> |
| 1406 | |
| 1407 | <listitem> |
| 1408 | <para> |
| 1409 | If HBA is in unknown state, reset both HBA and device. |
| 1410 | </para> |
| 1411 | </listitem> |
| 1412 | |
| 1413 | </itemizedlist> |
| 1414 | |
| 1415 | <para> |
| 1416 | HBA resetting is implementation specific. For a controller |
| 1417 | complying to taskfile/BMDMA PCI IDE, stopping active DMA |
| 1418 | transaction may be sufficient iff BMDMA state is the only HBA |
| 1419 | context. But even mostly taskfile/BMDMA PCI IDE complying |
| 1420 | controllers may have implementation specific requirements and |
| 1421 | mechanism to reset themselves. This must be addressed by |
| 1422 | specific drivers. |
| 1423 | </para> |
| 1424 | |
| 1425 | <para> |
| 1426 | OTOH, ATA/ATAPI standard describes in detail ways to reset |
| 1427 | ATA/ATAPI devices. |
| 1428 | </para> |
| 1429 | |
| 1430 | <variablelist> |
| 1431 | |
| 1432 | <varlistentry><term>PATA hardware reset</term> |
| 1433 | <listitem> |
| 1434 | <para> |
| 1435 | This is hardware initiated device reset signalled with |
| 1436 | asserted PATA RESET- signal. There is no standard way to |
| 1437 | initiate hardware reset from software although some |
| 1438 | hardware provides registers that allow driver to directly |
| 1439 | tweak the RESET- signal. |
| 1440 | </para> |
| 1441 | </listitem> |
| 1442 | </varlistentry> |
| 1443 | |
| 1444 | <varlistentry><term>Software reset</term> |
| 1445 | <listitem> |
| 1446 | <para> |
| 1447 | This is achieved by turning CONTROL SRST bit on for at |
| 1448 | least 5us. Both PATA and SATA support it but, in case of |
| 1449 | SATA, this may require controller-specific support as the |
| 1450 | second Register FIS to clear SRST should be transmitted |
| 1451 | while BSY bit is still set. Note that on PATA, this resets |
| 1452 | both master and slave devices on a channel. |
| 1453 | </para> |
| 1454 | </listitem> |
| 1455 | </varlistentry> |
| 1456 | |
| 1457 | <varlistentry><term>EXECUTE DEVICE DIAGNOSTIC command</term> |
| 1458 | <listitem> |
| 1459 | <para> |
| 1460 | Although ATA/ATAPI standard doesn't describe exactly, EDD |
| 1461 | implies some level of resetting, possibly similar level |
| 1462 | with software reset. Host-side EDD protocol can be handled |
| 1463 | with normal command processing and most SATA controllers |
| 1464 | should be able to handle EDD's just like other commands. |
| 1465 | As in software reset, EDD affects both devices on a PATA |
| 1466 | bus. |
| 1467 | </para> |
| 1468 | <para> |
| 1469 | Although EDD does reset devices, this doesn't suit error |
| 1470 | handling as EDD cannot be issued while BSY is set and it's |
| 1471 | unclear how it will act when device is in unknown/weird |
| 1472 | state. |
| 1473 | </para> |
| 1474 | </listitem> |
| 1475 | </varlistentry> |
| 1476 | |
| 1477 | <varlistentry><term>ATAPI DEVICE RESET command</term> |
| 1478 | <listitem> |
| 1479 | <para> |
| 1480 | This is very similar to software reset except that reset |
| 1481 | can be restricted to the selected device without affecting |
| 1482 | the other device sharing the cable. |
| 1483 | </para> |
| 1484 | </listitem> |
| 1485 | </varlistentry> |
| 1486 | |
| 1487 | <varlistentry><term>SATA phy reset</term> |
| 1488 | <listitem> |
| 1489 | <para> |
| 1490 | This is the preferred way of resetting a SATA device. In |
| 1491 | effect, it's identical to PATA hardware reset. Note that |
| 1492 | this can be done with the standard SCR Control register. |
| 1493 | As such, it's usually easier to implement than software |
| 1494 | reset. |
| 1495 | </para> |
| 1496 | </listitem> |
| 1497 | </varlistentry> |
| 1498 | |
| 1499 | </variablelist> |
| 1500 | |
| 1501 | <para> |
| 1502 | One more thing to consider when resetting devices is that |
| 1503 | resetting clears certain configuration parameters and they |
| 1504 | need to be set to their previous or newly adjusted values |
| 1505 | after reset. |
| 1506 | </para> |
| 1507 | |
| 1508 | <para> |
| 1509 | Parameters affected are. |
| 1510 | </para> |
| 1511 | |
| 1512 | <itemizedlist> |
| 1513 | |
| 1514 | <listitem> |
| 1515 | <para> |
| 1516 | CHS set up with INITIALIZE DEVICE PARAMETERS (seldomly used) |
| 1517 | </para> |
| 1518 | </listitem> |
| 1519 | |
| 1520 | <listitem> |
| 1521 | <para> |
| 1522 | Parameters set with SET FEATURES including transfer mode setting |
| 1523 | </para> |
| 1524 | </listitem> |
| 1525 | |
| 1526 | <listitem> |
| 1527 | <para> |
| 1528 | Block count set with SET MULTIPLE MODE |
| 1529 | </para> |
| 1530 | </listitem> |
| 1531 | |
| 1532 | <listitem> |
| 1533 | <para> |
| 1534 | Other parameters (SET MAX, MEDIA LOCK...) |
| 1535 | </para> |
| 1536 | </listitem> |
| 1537 | |
| 1538 | </itemizedlist> |
| 1539 | |
| 1540 | <para> |
| 1541 | ATA/ATAPI standard specifies that some parameters must be |
| 1542 | maintained across hardware or software reset, but doesn't |
| 1543 | strictly specify all of them. Always reconfiguring needed |
| 1544 | parameters after reset is required for robustness. Note that |
| 1545 | this also applies when resuming from deep sleep (power-off). |
| 1546 | </para> |
| 1547 | |
| 1548 | <para> |
| 1549 | Also, ATA/ATAPI standard requires that IDENTIFY DEVICE / |
| 1550 | IDENTIFY PACKET DEVICE is issued after any configuration |
| 1551 | parameter is updated or a hardware reset and the result used |
| 1552 | for further operation. OS driver is required to implement |
| 1553 | revalidation mechanism to support this. |
| 1554 | </para> |
| 1555 | |
| 1556 | </sect2> |
| 1557 | |
| 1558 | <sect2 id="exrecReconf"> |
| 1559 | <title>Reconfigure transport</title> |
| 1560 | |
| 1561 | <para> |
| 1562 | For both PATA and SATA, a lot of corners are cut for cheap |
| 1563 | connectors, cables or controllers and it's quite common to see |
| 1564 | high transmission error rate. This can be mitigated by |
| 1565 | lowering transmission speed. |
| 1566 | </para> |
| 1567 | |
| 1568 | <para> |
| 1569 | The following is a possible scheme Jeff Garzik suggested. |
| 1570 | </para> |
| 1571 | |
| 1572 | <blockquote> |
| 1573 | <para> |
| 1574 | If more than $N (3?) transmission errors happen in 15 minutes, |
| 1575 | </para> |
| 1576 | <itemizedlist> |
| 1577 | <listitem> |
| 1578 | <para> |
| 1579 | if SATA, decrease SATA PHY speed. if speed cannot be decreased, |
| 1580 | </para> |
| 1581 | </listitem> |
| 1582 | <listitem> |
| 1583 | <para> |
| 1584 | decrease UDMA xfer speed. if at UDMA0, switch to PIO4, |
| 1585 | </para> |
| 1586 | </listitem> |
| 1587 | <listitem> |
| 1588 | <para> |
| 1589 | decrease PIO xfer speed. if at PIO3, complain, but continue |
| 1590 | </para> |
| 1591 | </listitem> |
| 1592 | </itemizedlist> |
| 1593 | </blockquote> |
| 1594 | |
| 1595 | </sect2> |
| 1596 | |
| 1597 | </sect1> |
| 1598 | |
| 1599 | </chapter> |
| 1600 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1601 | <chapter id="PiixInt"> |
| 1602 | <title>ata_piix Internals</title> |
Henrik Kretzschmar | 58707cc | 2006-08-21 18:39:26 -0700 | [diff] [blame] | 1603 | !Idrivers/ata/ata_piix.c |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1604 | </chapter> |
| 1605 | |
| 1606 | <chapter id="SILInt"> |
| 1607 | <title>sata_sil Internals</title> |
Henrik Kretzschmar | 58707cc | 2006-08-21 18:39:26 -0700 | [diff] [blame] | 1608 | !Idrivers/ata/sata_sil.c |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1609 | </chapter> |
| 1610 | |
Jeff Garzik | 0cba632 | 2005-05-30 19:49:12 -0400 | [diff] [blame] | 1611 | <chapter id="libataThanks"> |
| 1612 | <title>Thanks</title> |
| 1613 | <para> |
| 1614 | The bulk of the ATA knowledge comes thanks to long conversations with |
| 1615 | Andre Hedrick (www.linux-ide.org), and long hours pondering the ATA |
| 1616 | and SCSI specifications. |
| 1617 | </para> |
| 1618 | <para> |
| 1619 | Thanks to Alan Cox for pointing out similarities |
| 1620 | between SATA and SCSI, and in general for motivation to hack on |
| 1621 | libata. |
| 1622 | </para> |
| 1623 | <para> |
| 1624 | libata's device detection |
| 1625 | method, ata_pio_devchk, and in general all the early probing was |
| 1626 | based on extensive study of Hale Landis's probe/reset code in his |
| 1627 | ATADRVR driver (www.ata-atapi.com). |
| 1628 | </para> |
| 1629 | </chapter> |
| 1630 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1631 | </book> |