Documentation/DocBook/libata.tmpl

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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
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<book id="libataDevGuide">
 <bookinfo>
  <title>libATA Developer's Guide</title>
  
  <authorgroup>
   <author>
    <firstname>Jeff</firstname>
    <surname>Garzik</surname>
   </author>
  </authorgroup>

  <copyright>
   <year>2003-2005</year>
   <holder>Jeff Garzik</holder>
  </copyright>

  <legalnotice>
   <para>
   The contents of this file are subject to the Open
   Software License version 1.1 that can be found at
   <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
   by reference.
   </para>

   <para>
   Alternatively, the contents of this file may be used under the terms
   of the GNU General Public License version 2 (the "GPL") as distributed
   in the kernel source COPYING file, in which case the provisions of
   the GPL are applicable instead of the above.  If you wish to allow
   the use of your version of this file only under the terms of the
   GPL and not to allow others to use your version of this file under
   the OSL, indicate your decision by deleting the provisions above and
   replace them with the notice and other provisions required by the GPL.
   If you do not delete the provisions above, a recipient may use your
   version of this file under either the OSL or the GPL.
   </para>

  </legalnotice>
 </bookinfo>

<toc></toc>

  <chapter id="libataIntroduction">
     <title>Introduction</title>
  <para>
  libATA is a library used inside the Linux kernel to support ATA host
  controllers and devices.  libATA provides an ATA driver API, class
  transports for ATA and ATAPI devices, and SCSI&lt;-&gt;ATA translation
  for ATA devices according to the T10 SAT specification.
  </para>
  <para>
  This Guide documents the libATA driver API, library functions, library
  internals, and a couple sample ATA low-level drivers.
  </para>
  </chapter>

  <chapter id="libataDriverApi">
     <title>libata Driver API</title>
     <para>
     struct ata_port_operations is defined for every low-level libata
     hardware driver, and it controls how the low-level driver
     interfaces with the ATA and SCSI layers.
     </para>
     <para>
     FIS-based drivers will hook into the system with ->qc_prep() and
     ->qc_issue() high-level hooks.  Hardware which behaves in a manner
     similar to PCI IDE hardware may utilize several generic helpers,
     defining at a bare minimum the bus I/O addresses of the ATA shadow
     register blocks.
     </para>
     <sect1>
        <title>struct ata_port_operations</title>

	<sect2><title>Disable ATA port</title>
	<programlisting>
void (*port_disable) (struct ata_port *);
	</programlisting>

	<para>
	Called from ata_bus_probe() and ata_bus_reset() error paths,
	as well as when unregistering from the SCSI module (rmmod, hot
	unplug).
	This function should do whatever needs to be done to take the
	port out of use.  In most cases, ata_port_disable() can be used
	as this hook.
	</para>
	<para>
	Called from ata_bus_probe() on a failed probe.
	Called from ata_bus_reset() on a failed bus reset.
	Called from ata_scsi_release().
	</para>

	</sect2>

	<sect2><title>Post-IDENTIFY device configuration</title>
	<programlisting>
void (*dev_config) (struct ata_port *, struct ata_device *);
	</programlisting>

	<para>
	Called after IDENTIFY [PACKET] DEVICE is issued to each device
	found.  Typically used to apply device-specific fixups prior to
	issue of SET FEATURES - XFER MODE, and prior to operation.
	</para>
	<para>
	Called by ata_device_add() after ata_dev_identify() determines
	a device is present.
	</para>
	<para>
	This entry may be specified as NULL in ata_port_operations.
	</para>

	</sect2>

	<sect2><title>Set PIO/DMA mode</title>
	<programlisting>
void (*set_piomode) (struct ata_port *, struct ata_device *);
void (*set_dmamode) (struct ata_port *, struct ata_device *);
void (*post_set_mode) (struct ata_port *ap);
	</programlisting>

	<para>
	Hooks called prior to the issue of SET FEATURES - XFER MODE
	command.  dev->pio_mode is guaranteed to be valid when
	->set_piomode() is called, and dev->dma_mode is guaranteed to be
	valid when ->set_dmamode() is called.  ->post_set_mode() is
	called unconditionally, after the SET FEATURES - XFER MODE
	command completes successfully.
	</para>

	<para>
	->set_piomode() is always called (if present), but
	->set_dma_mode() is only called if DMA is possible.
	</para>

	</sect2>

	<sect2><title>Taskfile read/write</title>
	<programlisting>
void (*tf_load) (struct ata_port *ap, struct ata_taskfile *tf);
void (*tf_read) (struct ata_port *ap, struct ata_taskfile *tf);
	</programlisting>

	<para>
	->tf_load() is called to load the given taskfile into hardware
	registers / DMA buffers.  ->tf_read() is called to read the
	hardware registers / DMA buffers, to obtain the current set of
	taskfile register values.
	Most drivers for taskfile-based hardware (PIO or MMIO) use
	ata_tf_load() and ata_tf_read() for these hooks.
	</para>

	</sect2>

	<sect2><title>ATA command execute</title>
	<programlisting>
void (*exec_command)(struct ata_port *ap, struct ata_taskfile *tf);
	</programlisting>

	<para>
	causes an ATA command, previously loaded with
	->tf_load(), to be initiated in hardware.
	Most drivers for taskfile-based hardware use ata_exec_command()
	for this hook.
	</para>

	</sect2>

	<sect2><title>Per-cmd ATAPI DMA capabilities filter</title>
	<programlisting>
int (*check_atapi_dma) (struct ata_queued_cmd *qc);
	</programlisting>

	<para>
Allow low-level driver to filter ATA PACKET commands, returning a status
indicating whether or not it is OK to use DMA for the supplied PACKET
command.
	</para>
	<para>
	This hook may be specified as NULL, in which case libata will
	assume that atapi dma can be supported.
	</para>

	</sect2>

	<sect2><title>Read specific ATA shadow registers</title>
	<programlisting>
u8   (*check_status)(struct ata_port *ap);
u8   (*check_altstatus)(struct ata_port *ap);
u8   (*check_err)(struct ata_port *ap);
	</programlisting>

	<para>
	Reads the Status/AltStatus/Error ATA shadow register from
	hardware.  On some hardware, reading the Status register has
	the side effect of clearing the interrupt condition.
	Most drivers for taskfile-based hardware use
	ata_check_status() for this hook.
	</para>
	<para>
	Note that because this is called from ata_device_add(), at
	least a dummy function that clears device interrupts must be
	provided for all drivers, even if the controller doesn't
	actually have a taskfile status register.
	</para>

	</sect2>

	<sect2><title>Select ATA device on bus</title>
	<programlisting>
void (*dev_select)(struct ata_port *ap, unsigned int device);
	</programlisting>

	<para>
	Issues the low-level hardware command(s) that causes one of N
	hardware devices to be considered 'selected' (active and
	available for use) on the ATA bus.  This generally has no
	meaning on FIS-based devices.
	</para>
	<para>
	Most drivers for taskfile-based hardware use
	ata_std_dev_select() for this hook.  Controllers which do not
	support second drives on a port (such as SATA contollers) will
	use ata_noop_dev_select().
	</para>

	</sect2>

	<sect2><title>Reset ATA bus</title>
	<programlisting>
void (*phy_reset) (struct ata_port *ap);
	</programlisting>

	<para>
	The very first step in the probe phase.  Actions vary depending
	on the bus type, typically.  After waking up the device and probing
	for device presence (PATA and SATA), typically a soft reset
	(SRST) will be performed.  Drivers typically use the helper
	functions ata_bus_reset() or sata_phy_reset() for this hook.
	Many SATA drivers use sata_phy_reset() or call it from within
	their own phy_reset() functions.
	</para>

	</sect2>

	<sect2><title>Control PCI IDE BMDMA engine</title>
	<programlisting>
void (*bmdma_setup) (struct ata_queued_cmd *qc);
void (*bmdma_start) (struct ata_queued_cmd *qc);
void (*bmdma_stop) (struct ata_port *ap);
u8   (*bmdma_status) (struct ata_port *ap);
	</programlisting>

	<para>
When setting up an IDE BMDMA transaction, these hooks arm
(->bmdma_setup), fire (->bmdma_start), and halt (->bmdma_stop)
the hardware's DMA engine.  ->bmdma_status is used to read the standard
PCI IDE DMA Status register.
	</para>

	<para>
These hooks are typically either no-ops, or simply not implemented, in
FIS-based drivers.
	</para>
	<para>
Most legacy IDE drivers use ata_bmdma_setup() for the bmdma_setup()
hook.  ata_bmdma_setup() will write the pointer to the PRD table to
the IDE PRD Table Address register, enable DMA in the DMA Command
register, and call exec_command() to begin the transfer.
	</para>
	<para>
Most legacy IDE drivers use ata_bmdma_start() for the bmdma_start()
hook.  ata_bmdma_start() will write the ATA_DMA_START flag to the DMA
Command register.
	</para>
	<para>
Many legacy IDE drivers use ata_bmdma_stop() for the bmdma_stop()
hook.  ata_bmdma_stop() clears the ATA_DMA_START flag in the DMA
command register.
	</para>
	<para>
Many legacy IDE drivers use ata_bmdma_status() as the bmdma_status() hook.
	</para>

	</sect2>

	<sect2><title>High-level taskfile hooks</title>
	<programlisting>
void (*qc_prep) (struct ata_queued_cmd *qc);
int (*qc_issue) (struct ata_queued_cmd *qc);
	</programlisting>

	<para>
	Higher-level hooks, these two hooks can potentially supercede
	several of the above taskfile/DMA engine hooks.  ->qc_prep is
	called after the buffers have been DMA-mapped, and is typically
	used to populate the hardware's DMA scatter-gather table.
	Most drivers use the standard ata_qc_prep() helper function, but
	more advanced drivers roll their own.
	</para>
	<para>
	->qc_issue is used to make a command active, once the hardware
	and S/G tables have been prepared.  IDE BMDMA drivers use the
	helper function ata_qc_issue_prot() for taskfile protocol-based
	dispatch.  More advanced drivers implement their own ->qc_issue.
	</para>
	<para>
	ata_qc_issue_prot() calls ->tf_load(), ->bmdma_setup(), and
	->bmdma_start() as necessary to initiate a transfer.
	</para>

	</sect2>

	<sect2><title>Timeout (error) handling</title>
	<programlisting>
void (*eng_timeout) (struct ata_port *ap);
	</programlisting>

	<para>
This is a high level error handling function, called from the
error handling thread, when a command times out.  Most newer
hardware will implement its own error handling code here.  IDE BMDMA
drivers may use the helper function ata_eng_timeout().
	</para>

	</sect2>

	<sect2><title>Hardware interrupt handling</title>
	<programlisting>
irqreturn_t (*irq_handler)(int, void *, struct pt_regs *);
void (*irq_clear) (struct ata_port *);
	</programlisting>

	<para>
	->irq_handler is the interrupt handling routine registered with
	the system, by libata.  ->irq_clear is called during probe just
	before the interrupt handler is registered, to be sure hardware
	is quiet.
	</para>
	<para>
	The second argument, dev_instance, should be cast to a pointer
	to struct ata_host_set.
	</para>
	<para>
	Most legacy IDE drivers use ata_interrupt() for the
	irq_handler hook, which scans all ports in the host_set,
	determines which queued command was active (if any), and calls
	ata_host_intr(ap,qc).
	</para>
	<para>
	Most legacy IDE drivers use ata_bmdma_irq_clear() for the
	irq_clear() hook, which simply clears the interrupt and error
	flags in the DMA status register.
	</para>

	</sect2>

	<sect2><title>SATA phy read/write</title>
	<programlisting>
u32 (*scr_read) (struct ata_port *ap, unsigned int sc_reg);
void (*scr_write) (struct ata_port *ap, unsigned int sc_reg,
                   u32 val);
	</programlisting>

	<para>
	Read and write standard SATA phy registers.  Currently only used
	if ->phy_reset hook called the sata_phy_reset() helper function.
	sc_reg is one of SCR_STATUS, SCR_CONTROL, SCR_ERROR, or SCR_ACTIVE.
	</para>

	</sect2>

	<sect2><title>Init and shutdown</title>
	<programlisting>
int (*port_start) (struct ata_port *ap);
void (*port_stop) (struct ata_port *ap);
void (*host_stop) (struct ata_host_set *host_set);
	</programlisting>

	<para>
	->port_start() is called just after the data structures for each
	port are initialized.  Typically this is used to alloc per-port
	DMA buffers / tables / rings, enable DMA engines, and similar
	tasks.  Some drivers also use this entry point as a chance to
	allocate driver-private memory for ap->private_data.
	</para>
	<para>
	Many drivers use ata_port_start() as this hook or call
	it from their own port_start() hooks.  ata_port_start()
	allocates space for a legacy IDE PRD table and returns.
	</para>
	<para>
	->port_stop() is called after ->host_stop().  It's sole function
	is to release DMA/memory resources, now that they are no longer
	actively being used.  Many drivers also free driver-private
	data from port at this time.
	</para>
	<para>
	Many drivers use ata_port_stop() as this hook, which frees the
	PRD table.
	</para>
	<para>
	->host_stop() is called after all ->port_stop() calls
have completed.  The hook must finalize hardware shutdown, release DMA
and other resources, etc.
	This hook may be specified as NULL, in which case it is not called.
	</para>

	</sect2>

     </sect1>
  </chapter>

  <chapter id="libataExt">
     <title>libata Library</title>
!Edrivers/scsi/libata-core.c
  </chapter>

  <chapter id="libataInt">
     <title>libata Core Internals</title>
!Idrivers/scsi/libata-core.c
  </chapter>

  <chapter id="libataScsiInt">
     <title>libata SCSI translation/emulation</title>
!Edrivers/scsi/libata-scsi.c
!Idrivers/scsi/libata-scsi.c
  </chapter>

  <chapter id="PiixInt">
     <title>ata_piix Internals</title>
!Idrivers/scsi/ata_piix.c
  </chapter>

  <chapter id="SILInt">
     <title>sata_sil Internals</title>
!Idrivers/scsi/sata_sil.c
  </chapter>

  <chapter id="libataThanks">
     <title>Thanks</title>
  <para>
  The bulk of the ATA knowledge comes thanks to long conversations with
  Andre Hedrick (www.linux-ide.org), and long hours pondering the ATA
  and SCSI specifications.
  </para>
  <para>
  Thanks to Alan Cox for pointing out similarities 
  between SATA and SCSI, and in general for motivation to hack on
  libata.
  </para>
  <para>
  libata's device detection
  method, ata_pio_devchk, and in general all the early probing was
  based on extensive study of Hale Landis's probe/reset code in his
  ATADRVR driver (www.ata-atapi.com).
  </para>
  </chapter>

</book>