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Linus Torvalds1da177e2005-04-16 15:20:36 -07001
2 Low Level Serial API
3 --------------------
4
5
Linus Torvalds1da177e2005-04-16 15:20:36 -07006This document is meant as a brief overview of some aspects of the new serial
7driver. It is not complete, any questions you have should be directed to
8<rmk@arm.linux.org.uk>
9
Russell King67ab7f52006-04-15 20:46:11 +010010The reference implementation is contained within amba_pl011.c.
Linus Torvalds1da177e2005-04-16 15:20:36 -070011
12
13
14Low Level Serial Hardware Driver
15--------------------------------
16
17The low level serial hardware driver is responsible for supplying port
18information (defined by uart_port) and a set of control methods (defined
19by uart_ops) to the core serial driver. The low level driver is also
20responsible for handling interrupts for the port, and providing any
21console support.
22
23
24Console Support
25---------------
26
27The serial core provides a few helper functions. This includes identifing
28the correct port structure (via uart_get_console) and decoding command line
29arguments (uart_parse_options).
30
Russell King67ab7f52006-04-15 20:46:11 +010031There is also a helper function (uart_write_console) which performs a
32character by character write, translating newlines to CRLF sequences.
33Driver writers are recommended to use this function rather than implementing
34their own version.
35
Linus Torvalds1da177e2005-04-16 15:20:36 -070036
37Locking
38-------
39
40It is the responsibility of the low level hardware driver to perform the
41necessary locking using port->lock. There are some exceptions (which
42are described in the uart_ops listing below.)
43
44There are three locks. A per-port spinlock, a per-port tmpbuf semaphore,
45and an overall semaphore.
46
47From the core driver perspective, the port->lock locks the following
48data:
49
50 port->mctrl
51 port->icount
52 info->xmit.head (circ->head)
53 info->xmit.tail (circ->tail)
54
55The low level driver is free to use this lock to provide any additional
56locking.
57
58The core driver uses the info->tmpbuf_sem lock to prevent multi-threaded
59access to the info->tmpbuf bouncebuffer used for port writes.
60
61The port_sem semaphore is used to protect against ports being added/
62removed or reconfigured at inappropriate times.
63
64
65uart_ops
66--------
67
68The uart_ops structure is the main interface between serial_core and the
69hardware specific driver. It contains all the methods to control the
70hardware.
71
72 tx_empty(port)
73 This function tests whether the transmitter fifo and shifter
74 for the port described by 'port' is empty. If it is empty,
75 this function should return TIOCSER_TEMT, otherwise return 0.
76 If the port does not support this operation, then it should
77 return TIOCSER_TEMT.
78
79 Locking: none.
80 Interrupts: caller dependent.
81 This call must not sleep
82
83 set_mctrl(port, mctrl)
84 This function sets the modem control lines for port described
85 by 'port' to the state described by mctrl. The relevant bits
86 of mctrl are:
87 - TIOCM_RTS RTS signal.
88 - TIOCM_DTR DTR signal.
89 - TIOCM_OUT1 OUT1 signal.
90 - TIOCM_OUT2 OUT2 signal.
Russell King67ab7f52006-04-15 20:46:11 +010091 - TIOCM_LOOP Set the port into loopback mode.
Linus Torvalds1da177e2005-04-16 15:20:36 -070092 If the appropriate bit is set, the signal should be driven
93 active. If the bit is clear, the signal should be driven
94 inactive.
95
96 Locking: port->lock taken.
97 Interrupts: locally disabled.
98 This call must not sleep
99
100 get_mctrl(port)
101 Returns the current state of modem control inputs. The state
102 of the outputs should not be returned, since the core keeps
103 track of their state. The state information should include:
104 - TIOCM_DCD state of DCD signal
105 - TIOCM_CTS state of CTS signal
106 - TIOCM_DSR state of DSR signal
107 - TIOCM_RI state of RI signal
108 The bit is set if the signal is currently driven active. If
109 the port does not support CTS, DCD or DSR, the driver should
110 indicate that the signal is permanently active. If RI is
111 not available, the signal should not be indicated as active.
112
Russell Kingc5f46442005-06-29 09:42:38 +0100113 Locking: port->lock taken.
114 Interrupts: locally disabled.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700115 This call must not sleep
116
Russell Kingb129a8c2005-08-31 10:12:14 +0100117 stop_tx(port)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700118 Stop transmitting characters. This might be due to the CTS
119 line becoming inactive or the tty layer indicating we want
Russell Kingb129a8c2005-08-31 10:12:14 +0100120 to stop transmission due to an XOFF character.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700121
Russell King6a8f8d72005-10-31 11:53:19 +0000122 The driver should stop transmitting characters as soon as
123 possible.
124
Linus Torvalds1da177e2005-04-16 15:20:36 -0700125 Locking: port->lock taken.
126 Interrupts: locally disabled.
127 This call must not sleep
128
Russell Kingb129a8c2005-08-31 10:12:14 +0100129 start_tx(port)
Russell King6a8f8d72005-10-31 11:53:19 +0000130 Start transmitting characters.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700131
132 Locking: port->lock taken.
133 Interrupts: locally disabled.
134 This call must not sleep
135
136 stop_rx(port)
137 Stop receiving characters; the port is in the process of
138 being closed.
139
140 Locking: port->lock taken.
141 Interrupts: locally disabled.
142 This call must not sleep
143
144 enable_ms(port)
145 Enable the modem status interrupts.
146
Russell King67ab7f52006-04-15 20:46:11 +0100147 This method may be called multiple times. Modem status
148 interrupts should be disabled when the shutdown method is
149 called.
150
Linus Torvalds1da177e2005-04-16 15:20:36 -0700151 Locking: port->lock taken.
152 Interrupts: locally disabled.
153 This call must not sleep
154
155 break_ctl(port,ctl)
156 Control the transmission of a break signal. If ctl is
157 nonzero, the break signal should be transmitted. The signal
158 should be terminated when another call is made with a zero
159 ctl.
160
161 Locking: none.
162 Interrupts: caller dependent.
163 This call must not sleep
164
165 startup(port)
166 Grab any interrupt resources and initialise any low level driver
167 state. Enable the port for reception. It should not activate
168 RTS nor DTR; this will be done via a separate call to set_mctrl.
169
Russell King67ab7f52006-04-15 20:46:11 +0100170 This method will only be called when the port is initially opened.
171
Linus Torvalds1da177e2005-04-16 15:20:36 -0700172 Locking: port_sem taken.
173 Interrupts: globally disabled.
174
175 shutdown(port)
176 Disable the port, disable any break condition that may be in
177 effect, and free any interrupt resources. It should not disable
178 RTS nor DTR; this will have already been done via a separate
179 call to set_mctrl.
180
Russell King67ab7f52006-04-15 20:46:11 +0100181 Drivers must not access port->info once this call has completed.
182
183 This method will only be called when there are no more users of
184 this port.
185
Linus Torvalds1da177e2005-04-16 15:20:36 -0700186 Locking: port_sem taken.
187 Interrupts: caller dependent.
188
Haavard Skinnemoen6bb0e3a2008-07-16 21:52:36 +0100189 flush_buffer(port)
190 Flush any write buffers, reset any DMA state and stop any
191 ongoing DMA transfers.
192
193 This will be called whenever the port->info->xmit circular
194 buffer is cleared.
195
196 Locking: port->lock taken.
197 Interrupts: locally disabled.
198 This call must not sleep
199
Linus Torvalds1da177e2005-04-16 15:20:36 -0700200 set_termios(port,termios,oldtermios)
201 Change the port parameters, including word length, parity, stop
202 bits. Update read_status_mask and ignore_status_mask to indicate
203 the types of events we are interested in receiving. Relevant
204 termios->c_cflag bits are:
205 CSIZE - word size
206 CSTOPB - 2 stop bits
207 PARENB - parity enable
208 PARODD - odd parity (when PARENB is in force)
209 CREAD - enable reception of characters (if not set,
210 still receive characters from the port, but
211 throw them away.
212 CRTSCTS - if set, enable CTS status change reporting
213 CLOCAL - if not set, enable modem status change
214 reporting.
215 Relevant termios->c_iflag bits are:
216 INPCK - enable frame and parity error events to be
217 passed to the TTY layer.
218 BRKINT
219 PARMRK - both of these enable break events to be
220 passed to the TTY layer.
221
222 IGNPAR - ignore parity and framing errors
223 IGNBRK - ignore break errors, If IGNPAR is also
224 set, ignore overrun errors as well.
225 The interaction of the iflag bits is as follows (parity error
226 given as an example):
227 Parity error INPCK IGNPAR
Peter Korsgaard89f3da32006-06-02 17:47:26 +0100228 n/a 0 n/a character received, marked as
Linus Torvalds1da177e2005-04-16 15:20:36 -0700229 TTY_NORMAL
Peter Korsgaard89f3da32006-06-02 17:47:26 +0100230 None 1 n/a character received, marked as
231 TTY_NORMAL
232 Yes 1 0 character received, marked as
Linus Torvalds1da177e2005-04-16 15:20:36 -0700233 TTY_PARITY
Peter Korsgaard89f3da32006-06-02 17:47:26 +0100234 Yes 1 1 character discarded
Linus Torvalds1da177e2005-04-16 15:20:36 -0700235
236 Other flags may be used (eg, xon/xoff characters) if your
237 hardware supports hardware "soft" flow control.
238
239 Locking: none.
240 Interrupts: caller dependent.
241 This call must not sleep
242
243 pm(port,state,oldstate)
244 Perform any power management related activities on the specified
245 port. State indicates the new state (defined by ACPI D0-D3),
246 oldstate indicates the previous state. Essentially, D0 means
247 fully on, D3 means powered down.
248
249 This function should not be used to grab any resources.
250
251 This will be called when the port is initially opened and finally
252 closed, except when the port is also the system console. This
253 will occur even if CONFIG_PM is not set.
254
255 Locking: none.
256 Interrupts: caller dependent.
257
258 type(port)
259 Return a pointer to a string constant describing the specified
260 port, or return NULL, in which case the string 'unknown' is
261 substituted.
262
263 Locking: none.
264 Interrupts: caller dependent.
265
266 release_port(port)
267 Release any memory and IO region resources currently in use by
268 the port.
269
270 Locking: none.
271 Interrupts: caller dependent.
272
273 request_port(port)
274 Request any memory and IO region resources required by the port.
275 If any fail, no resources should be registered when this function
276 returns, and it should return -EBUSY on failure.
277
278 Locking: none.
279 Interrupts: caller dependent.
280
281 config_port(port,type)
282 Perform any autoconfiguration steps required for the port. `type`
283 contains a bit mask of the required configuration. UART_CONFIG_TYPE
284 indicates that the port requires detection and identification.
285 port->type should be set to the type found, or PORT_UNKNOWN if
286 no port was detected.
287
288 UART_CONFIG_IRQ indicates autoconfiguration of the interrupt signal,
289 which should be probed using standard kernel autoprobing techniques.
290 This is not necessary on platforms where ports have interrupts
291 internally hard wired (eg, system on a chip implementations).
292
293 Locking: none.
294 Interrupts: caller dependent.
295
296 verify_port(port,serinfo)
297 Verify the new serial port information contained within serinfo is
298 suitable for this port type.
299
300 Locking: none.
301 Interrupts: caller dependent.
302
303 ioctl(port,cmd,arg)
304 Perform any port specific IOCTLs. IOCTL commands must be defined
305 using the standard numbering system found in <asm/ioctl.h>
306
307 Locking: none.
308 Interrupts: caller dependent.
309
310Other functions
311---------------
312
Russell King6a8f8d72005-10-31 11:53:19 +0000313uart_update_timeout(port,cflag,baud)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700314 Update the FIFO drain timeout, port->timeout, according to the
Russell King6a8f8d72005-10-31 11:53:19 +0000315 number of bits, parity, stop bits and baud rate.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700316
317 Locking: caller is expected to take port->lock
318 Interrupts: n/a
319
Russell King6a8f8d72005-10-31 11:53:19 +0000320uart_get_baud_rate(port,termios,old,min,max)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700321 Return the numeric baud rate for the specified termios, taking
322 account of the special 38400 baud "kludge". The B0 baud rate
323 is mapped to 9600 baud.
324
Russell King6a8f8d72005-10-31 11:53:19 +0000325 If the baud rate is not within min..max, then if old is non-NULL,
326 the original baud rate will be tried. If that exceeds the
327 min..max constraint, 9600 baud will be returned. termios will
328 be updated to the baud rate in use.
329
330 Note: min..max must always allow 9600 baud to be selected.
331
Linus Torvalds1da177e2005-04-16 15:20:36 -0700332 Locking: caller dependent.
333 Interrupts: n/a
334
Russell King6a8f8d72005-10-31 11:53:19 +0000335uart_get_divisor(port,baud)
336 Return the divsor (baud_base / baud) for the specified baud
337 rate, appropriately rounded.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700338
339 If 38400 baud and custom divisor is selected, return the
340 custom divisor instead.
341
342 Locking: caller dependent.
343 Interrupts: n/a
344
Russell King6a8f8d72005-10-31 11:53:19 +0000345uart_match_port(port1,port2)
346 This utility function can be used to determine whether two
347 uart_port structures describe the same port.
348
349 Locking: n/a
350 Interrupts: n/a
351
352uart_write_wakeup(port)
353 A driver is expected to call this function when the number of
354 characters in the transmit buffer have dropped below a threshold.
355
356 Locking: port->lock should be held.
357 Interrupts: n/a
358
359uart_register_driver(drv)
360 Register a uart driver with the core driver. We in turn register
361 with the tty layer, and initialise the core driver per-port state.
362
363 drv->port should be NULL, and the per-port structures should be
364 registered using uart_add_one_port after this call has succeeded.
365
366 Locking: none
367 Interrupts: enabled
368
369uart_unregister_driver()
370 Remove all references to a driver from the core driver. The low
371 level driver must have removed all its ports via the
372 uart_remove_one_port() if it registered them with uart_add_one_port().
373
374 Locking: none
375 Interrupts: enabled
376
377uart_suspend_port()
378
379uart_resume_port()
380
381uart_add_one_port()
382
383uart_remove_one_port()
384
Linus Torvalds1da177e2005-04-16 15:20:36 -0700385Other notes
386-----------
387
388It is intended some day to drop the 'unused' entries from uart_port, and
389allow low level drivers to register their own individual uart_port's with
390the core. This will allow drivers to use uart_port as a pointer to a
391structure containing both the uart_port entry with their own extensions,
392thus:
393
394 struct my_port {
395 struct uart_port port;
396 int my_stuff;
397 };