Loading...
1
2 Low Level Serial API
3 --------------------
4
5
6This 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
10The reference implementation is contained within amba_pl011.c.
11
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
31There is also a helper function (uart_console_write) 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
36
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 two locks. A per-port spinlock, and an overall semaphore.
45
46From the core driver perspective, the port->lock locks the following
47data:
48
49 port->mctrl
50 port->icount
51 port->state->xmit.head (circ_buf->head)
52 port->state->xmit.tail (circ_buf->tail)
53
54The low level driver is free to use this lock to provide any additional
55locking.
56
57The port_sem semaphore is used to protect against ports being added/
58removed or reconfigured at inappropriate times. Since v2.6.27, this
59semaphore has been the 'mutex' member of the tty_port struct, and
60commonly referred to as the port mutex.
61
62
63uart_ops
64--------
65
66The uart_ops structure is the main interface between serial_core and the
67hardware specific driver. It contains all the methods to control the
68hardware.
69
70 tx_empty(port)
71 This function tests whether the transmitter fifo and shifter
72 for the port described by 'port' is empty. If it is empty,
73 this function should return TIOCSER_TEMT, otherwise return 0.
74 If the port does not support this operation, then it should
75 return TIOCSER_TEMT.
76
77 Locking: none.
78 Interrupts: caller dependent.
79 This call must not sleep
80
81 set_mctrl(port, mctrl)
82 This function sets the modem control lines for port described
83 by 'port' to the state described by mctrl. The relevant bits
84 of mctrl are:
85 - TIOCM_RTS RTS signal.
86 - TIOCM_DTR DTR signal.
87 - TIOCM_OUT1 OUT1 signal.
88 - TIOCM_OUT2 OUT2 signal.
89 - TIOCM_LOOP Set the port into loopback mode.
90 If the appropriate bit is set, the signal should be driven
91 active. If the bit is clear, the signal should be driven
92 inactive.
93
94 Locking: port->lock taken.
95 Interrupts: locally disabled.
96 This call must not sleep
97
98 get_mctrl(port)
99 Returns the current state of modem control inputs. The state
100 of the outputs should not be returned, since the core keeps
101 track of their state. The state information should include:
102 - TIOCM_CAR state of DCD signal
103 - TIOCM_CTS state of CTS signal
104 - TIOCM_DSR state of DSR signal
105 - TIOCM_RI state of RI signal
106 The bit is set if the signal is currently driven active. If
107 the port does not support CTS, DCD or DSR, the driver should
108 indicate that the signal is permanently active. If RI is
109 not available, the signal should not be indicated as active.
110
111 Locking: port->lock taken.
112 Interrupts: locally disabled.
113 This call must not sleep
114
115 stop_tx(port)
116 Stop transmitting characters. This might be due to the CTS
117 line becoming inactive or the tty layer indicating we want
118 to stop transmission due to an XOFF character.
119
120 The driver should stop transmitting characters as soon as
121 possible.
122
123 Locking: port->lock taken.
124 Interrupts: locally disabled.
125 This call must not sleep
126
127 start_tx(port)
128 Start transmitting characters.
129
130 Locking: port->lock taken.
131 Interrupts: locally disabled.
132 This call must not sleep
133
134 throttle(port)
135 Notify the serial driver that input buffers for the line discipline are
136 close to full, and it should somehow signal that no more characters
137 should be sent to the serial port.
138 This will be called only if hardware assisted flow control is enabled.
139
140 Locking: serialized with .unthrottle() and termios modification by the
141 tty layer.
142
143 unthrottle(port)
144 Notify the serial driver that characters can now be sent to the serial
145 port without fear of overrunning the input buffers of the line
146 disciplines.
147 This will be called only if hardware assisted flow control is enabled.
148
149 Locking: serialized with .throttle() and termios modification by the
150 tty layer.
151
152 send_xchar(port,ch)
153 Transmit a high priority character, even if the port is stopped.
154 This is used to implement XON/XOFF flow control and tcflow(). If
155 the serial driver does not implement this function, the tty core
156 will append the character to the circular buffer and then call
157 start_tx() / stop_tx() to flush the data out.
158
159 Do not transmit if ch == '\0' (__DISABLED_CHAR).
160
161 Locking: none.
162 Interrupts: caller dependent.
163
164 stop_rx(port)
165 Stop receiving characters; the port is in the process of
166 being closed.
167
168 Locking: port->lock taken.
169 Interrupts: locally disabled.
170 This call must not sleep
171
172 enable_ms(port)
173 Enable the modem status interrupts.
174
175 This method may be called multiple times. Modem status
176 interrupts should be disabled when the shutdown method is
177 called.
178
179 Locking: port->lock taken.
180 Interrupts: locally disabled.
181 This call must not sleep
182
183 break_ctl(port,ctl)
184 Control the transmission of a break signal. If ctl is
185 nonzero, the break signal should be transmitted. The signal
186 should be terminated when another call is made with a zero
187 ctl.
188
189 Locking: caller holds tty_port->mutex
190
191 startup(port)
192 Grab any interrupt resources and initialise any low level driver
193 state. Enable the port for reception. It should not activate
194 RTS nor DTR; this will be done via a separate call to set_mctrl.
195
196 This method will only be called when the port is initially opened.
197
198 Locking: port_sem taken.
199 Interrupts: globally disabled.
200
201 shutdown(port)
202 Disable the port, disable any break condition that may be in
203 effect, and free any interrupt resources. It should not disable
204 RTS nor DTR; this will have already been done via a separate
205 call to set_mctrl.
206
207 Drivers must not access port->state once this call has completed.
208
209 This method will only be called when there are no more users of
210 this port.
211
212 Locking: port_sem taken.
213 Interrupts: caller dependent.
214
215 flush_buffer(port)
216 Flush any write buffers, reset any DMA state and stop any
217 ongoing DMA transfers.
218
219 This will be called whenever the port->state->xmit circular
220 buffer is cleared.
221
222 Locking: port->lock taken.
223 Interrupts: locally disabled.
224 This call must not sleep
225
226 set_termios(port,termios,oldtermios)
227 Change the port parameters, including word length, parity, stop
228 bits. Update read_status_mask and ignore_status_mask to indicate
229 the types of events we are interested in receiving. Relevant
230 termios->c_cflag bits are:
231 CSIZE - word size
232 CSTOPB - 2 stop bits
233 PARENB - parity enable
234 PARODD - odd parity (when PARENB is in force)
235 CREAD - enable reception of characters (if not set,
236 still receive characters from the port, but
237 throw them away.
238 CRTSCTS - if set, enable CTS status change reporting
239 CLOCAL - if not set, enable modem status change
240 reporting.
241 Relevant termios->c_iflag bits are:
242 INPCK - enable frame and parity error events to be
243 passed to the TTY layer.
244 BRKINT
245 PARMRK - both of these enable break events to be
246 passed to the TTY layer.
247
248 IGNPAR - ignore parity and framing errors
249 IGNBRK - ignore break errors, If IGNPAR is also
250 set, ignore overrun errors as well.
251 The interaction of the iflag bits is as follows (parity error
252 given as an example):
253 Parity error INPCK IGNPAR
254 n/a 0 n/a character received, marked as
255 TTY_NORMAL
256 None 1 n/a character received, marked as
257 TTY_NORMAL
258 Yes 1 0 character received, marked as
259 TTY_PARITY
260 Yes 1 1 character discarded
261
262 Other flags may be used (eg, xon/xoff characters) if your
263 hardware supports hardware "soft" flow control.
264
265 Locking: caller holds tty_port->mutex
266 Interrupts: caller dependent.
267 This call must not sleep
268
269 set_ldisc(port,termios)
270 Notifier for discipline change. See Documentation/serial/tty.txt.
271
272 Locking: caller holds tty_port->mutex
273
274 pm(port,state,oldstate)
275 Perform any power management related activities on the specified
276 port. State indicates the new state (defined by
277 enum uart_pm_state), oldstate indicates the previous state.
278
279 This function should not be used to grab any resources.
280
281 This will be called when the port is initially opened and finally
282 closed, except when the port is also the system console. This
283 will occur even if CONFIG_PM is not set.
284
285 Locking: none.
286 Interrupts: caller dependent.
287
288 type(port)
289 Return a pointer to a string constant describing the specified
290 port, or return NULL, in which case the string 'unknown' is
291 substituted.
292
293 Locking: none.
294 Interrupts: caller dependent.
295
296 release_port(port)
297 Release any memory and IO region resources currently in use by
298 the port.
299
300 Locking: none.
301 Interrupts: caller dependent.
302
303 request_port(port)
304 Request any memory and IO region resources required by the port.
305 If any fail, no resources should be registered when this function
306 returns, and it should return -EBUSY on failure.
307
308 Locking: none.
309 Interrupts: caller dependent.
310
311 config_port(port,type)
312 Perform any autoconfiguration steps required for the port. `type`
313 contains a bit mask of the required configuration. UART_CONFIG_TYPE
314 indicates that the port requires detection and identification.
315 port->type should be set to the type found, or PORT_UNKNOWN if
316 no port was detected.
317
318 UART_CONFIG_IRQ indicates autoconfiguration of the interrupt signal,
319 which should be probed using standard kernel autoprobing techniques.
320 This is not necessary on platforms where ports have interrupts
321 internally hard wired (eg, system on a chip implementations).
322
323 Locking: none.
324 Interrupts: caller dependent.
325
326 verify_port(port,serinfo)
327 Verify the new serial port information contained within serinfo is
328 suitable for this port type.
329
330 Locking: none.
331 Interrupts: caller dependent.
332
333 ioctl(port,cmd,arg)
334 Perform any port specific IOCTLs. IOCTL commands must be defined
335 using the standard numbering system found in <asm/ioctl.h>
336
337 Locking: none.
338 Interrupts: caller dependent.
339
340 poll_init(port)
341 Called by kgdb to perform the minimal hardware initialization needed
342 to support poll_put_char() and poll_get_char(). Unlike ->startup()
343 this should not request interrupts.
344
345 Locking: tty_mutex and tty_port->mutex taken.
346 Interrupts: n/a.
347
348 poll_put_char(port,ch)
349 Called by kgdb to write a single character directly to the serial
350 port. It can and should block until there is space in the TX FIFO.
351
352 Locking: none.
353 Interrupts: caller dependent.
354 This call must not sleep
355
356 poll_get_char(port)
357 Called by kgdb to read a single character directly from the serial
358 port. If data is available, it should be returned; otherwise
359 the function should return NO_POLL_CHAR immediately.
360
361 Locking: none.
362 Interrupts: caller dependent.
363 This call must not sleep
364
365Other functions
366---------------
367
368uart_update_timeout(port,cflag,baud)
369 Update the FIFO drain timeout, port->timeout, according to the
370 number of bits, parity, stop bits and baud rate.
371
372 Locking: caller is expected to take port->lock
373 Interrupts: n/a
374
375uart_get_baud_rate(port,termios,old,min,max)
376 Return the numeric baud rate for the specified termios, taking
377 account of the special 38400 baud "kludge". The B0 baud rate
378 is mapped to 9600 baud.
379
380 If the baud rate is not within min..max, then if old is non-NULL,
381 the original baud rate will be tried. If that exceeds the
382 min..max constraint, 9600 baud will be returned. termios will
383 be updated to the baud rate in use.
384
385 Note: min..max must always allow 9600 baud to be selected.
386
387 Locking: caller dependent.
388 Interrupts: n/a
389
390uart_get_divisor(port,baud)
391 Return the divisor (baud_base / baud) for the specified baud
392 rate, appropriately rounded.
393
394 If 38400 baud and custom divisor is selected, return the
395 custom divisor instead.
396
397 Locking: caller dependent.
398 Interrupts: n/a
399
400uart_match_port(port1,port2)
401 This utility function can be used to determine whether two
402 uart_port structures describe the same port.
403
404 Locking: n/a
405 Interrupts: n/a
406
407uart_write_wakeup(port)
408 A driver is expected to call this function when the number of
409 characters in the transmit buffer have dropped below a threshold.
410
411 Locking: port->lock should be held.
412 Interrupts: n/a
413
414uart_register_driver(drv)
415 Register a uart driver with the core driver. We in turn register
416 with the tty layer, and initialise the core driver per-port state.
417
418 drv->port should be NULL, and the per-port structures should be
419 registered using uart_add_one_port after this call has succeeded.
420
421 Locking: none
422 Interrupts: enabled
423
424uart_unregister_driver()
425 Remove all references to a driver from the core driver. The low
426 level driver must have removed all its ports via the
427 uart_remove_one_port() if it registered them with uart_add_one_port().
428
429 Locking: none
430 Interrupts: enabled
431
432uart_suspend_port()
433
434uart_resume_port()
435
436uart_add_one_port()
437
438uart_remove_one_port()
439
440Other notes
441-----------
442
443It is intended some day to drop the 'unused' entries from uart_port, and
444allow low level drivers to register their own individual uart_port's with
445the core. This will allow drivers to use uart_port as a pointer to a
446structure containing both the uart_port entry with their own extensions,
447thus:
448
449 struct my_port {
450 struct uart_port port;
451 int my_stuff;
452 };
453
454Modem control lines via GPIO
455----------------------------
456
457Some helpers are provided in order to set/get modem control lines via GPIO.
458
459mctrl_gpio_init(port, idx):
460 This will get the {cts,rts,...}-gpios from device tree if they are
461 present and request them, set direction etc, and return an
462 allocated structure. devm_* functions are used, so there's no need
463 to call mctrl_gpio_free().
464 As this sets up the irq handling make sure to not handle changes to the
465 gpio input lines in your driver, too.
466
467mctrl_gpio_free(dev, gpios):
468 This will free the requested gpios in mctrl_gpio_init().
469 As devm_* functions are used, there's generally no need to call
470 this function.
471
472mctrl_gpio_to_gpiod(gpios, gidx)
473 This returns the gpio_desc structure associated to the modem line
474 index.
475
476mctrl_gpio_set(gpios, mctrl):
477 This will sets the gpios according to the mctrl state.
478
479mctrl_gpio_get(gpios, mctrl):
480 This will update mctrl with the gpios values.
481
482mctrl_gpio_enable_ms(gpios):
483 Enables irqs and handling of changes to the ms lines.
484
485mctrl_gpio_disable_ms(gpios):
486 Disables irqs and handling of changes to the ms lines.
1
2 Low Level Serial API
3 --------------------
4
5
6This 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
10The reference implementation is contained within amba_pl011.c.
11
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
31There 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
36
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. Since v2.6.27, this
63semaphore has been the 'mutex' member of the tty_port struct, and
64commonly referred to as the port mutex (or port->mutex).
65
66
67uart_ops
68--------
69
70The uart_ops structure is the main interface between serial_core and the
71hardware specific driver. It contains all the methods to control the
72hardware.
73
74 tx_empty(port)
75 This function tests whether the transmitter fifo and shifter
76 for the port described by 'port' is empty. If it is empty,
77 this function should return TIOCSER_TEMT, otherwise return 0.
78 If the port does not support this operation, then it should
79 return TIOCSER_TEMT.
80
81 Locking: none.
82 Interrupts: caller dependent.
83 This call must not sleep
84
85 set_mctrl(port, mctrl)
86 This function sets the modem control lines for port described
87 by 'port' to the state described by mctrl. The relevant bits
88 of mctrl are:
89 - TIOCM_RTS RTS signal.
90 - TIOCM_DTR DTR signal.
91 - TIOCM_OUT1 OUT1 signal.
92 - TIOCM_OUT2 OUT2 signal.
93 - TIOCM_LOOP Set the port into loopback mode.
94 If the appropriate bit is set, the signal should be driven
95 active. If the bit is clear, the signal should be driven
96 inactive.
97
98 Locking: port->lock taken.
99 Interrupts: locally disabled.
100 This call must not sleep
101
102 get_mctrl(port)
103 Returns the current state of modem control inputs. The state
104 of the outputs should not be returned, since the core keeps
105 track of their state. The state information should include:
106 - TIOCM_CAR state of DCD signal
107 - TIOCM_CTS state of CTS signal
108 - TIOCM_DSR state of DSR signal
109 - TIOCM_RI state of RI signal
110 The bit is set if the signal is currently driven active. If
111 the port does not support CTS, DCD or DSR, the driver should
112 indicate that the signal is permanently active. If RI is
113 not available, the signal should not be indicated as active.
114
115 Locking: port->lock taken.
116 Interrupts: locally disabled.
117 This call must not sleep
118
119 stop_tx(port)
120 Stop transmitting characters. This might be due to the CTS
121 line becoming inactive or the tty layer indicating we want
122 to stop transmission due to an XOFF character.
123
124 The driver should stop transmitting characters as soon as
125 possible.
126
127 Locking: port->lock taken.
128 Interrupts: locally disabled.
129 This call must not sleep
130
131 start_tx(port)
132 Start transmitting characters.
133
134 Locking: port->lock taken.
135 Interrupts: locally disabled.
136 This call must not sleep
137
138 send_xchar(port,ch)
139 Transmit a high priority character, even if the port is stopped.
140 This is used to implement XON/XOFF flow control and tcflow(). If
141 the serial driver does not implement this function, the tty core
142 will append the character to the circular buffer and then call
143 start_tx() / stop_tx() to flush the data out.
144
145 Do not transmit if ch == '\0' (__DISABLED_CHAR).
146
147 Locking: none.
148 Interrupts: caller dependent.
149
150 stop_rx(port)
151 Stop receiving characters; the port is in the process of
152 being closed.
153
154 Locking: port->lock taken.
155 Interrupts: locally disabled.
156 This call must not sleep
157
158 enable_ms(port)
159 Enable the modem status interrupts.
160
161 This method may be called multiple times. Modem status
162 interrupts should be disabled when the shutdown method is
163 called.
164
165 Locking: port->lock taken.
166 Interrupts: locally disabled.
167 This call must not sleep
168
169 break_ctl(port,ctl)
170 Control the transmission of a break signal. If ctl is
171 nonzero, the break signal should be transmitted. The signal
172 should be terminated when another call is made with a zero
173 ctl.
174
175 Locking: none.
176 Interrupts: caller dependent.
177 This call must not sleep
178
179 startup(port)
180 Grab any interrupt resources and initialise any low level driver
181 state. Enable the port for reception. It should not activate
182 RTS nor DTR; this will be done via a separate call to set_mctrl.
183
184 This method will only be called when the port is initially opened.
185
186 Locking: port_sem taken.
187 Interrupts: globally disabled.
188
189 shutdown(port)
190 Disable the port, disable any break condition that may be in
191 effect, and free any interrupt resources. It should not disable
192 RTS nor DTR; this will have already been done via a separate
193 call to set_mctrl.
194
195 Drivers must not access port->info once this call has completed.
196
197 This method will only be called when there are no more users of
198 this port.
199
200 Locking: port_sem taken.
201 Interrupts: caller dependent.
202
203 flush_buffer(port)
204 Flush any write buffers, reset any DMA state and stop any
205 ongoing DMA transfers.
206
207 This will be called whenever the port->info->xmit circular
208 buffer is cleared.
209
210 Locking: port->lock taken.
211 Interrupts: locally disabled.
212 This call must not sleep
213
214 set_termios(port,termios,oldtermios)
215 Change the port parameters, including word length, parity, stop
216 bits. Update read_status_mask and ignore_status_mask to indicate
217 the types of events we are interested in receiving. Relevant
218 termios->c_cflag bits are:
219 CSIZE - word size
220 CSTOPB - 2 stop bits
221 PARENB - parity enable
222 PARODD - odd parity (when PARENB is in force)
223 CREAD - enable reception of characters (if not set,
224 still receive characters from the port, but
225 throw them away.
226 CRTSCTS - if set, enable CTS status change reporting
227 CLOCAL - if not set, enable modem status change
228 reporting.
229 Relevant termios->c_iflag bits are:
230 INPCK - enable frame and parity error events to be
231 passed to the TTY layer.
232 BRKINT
233 PARMRK - both of these enable break events to be
234 passed to the TTY layer.
235
236 IGNPAR - ignore parity and framing errors
237 IGNBRK - ignore break errors, If IGNPAR is also
238 set, ignore overrun errors as well.
239 The interaction of the iflag bits is as follows (parity error
240 given as an example):
241 Parity error INPCK IGNPAR
242 n/a 0 n/a character received, marked as
243 TTY_NORMAL
244 None 1 n/a character received, marked as
245 TTY_NORMAL
246 Yes 1 0 character received, marked as
247 TTY_PARITY
248 Yes 1 1 character discarded
249
250 Other flags may be used (eg, xon/xoff characters) if your
251 hardware supports hardware "soft" flow control.
252
253 Locking: caller holds port->mutex
254 Interrupts: caller dependent.
255 This call must not sleep
256
257 pm(port,state,oldstate)
258 Perform any power management related activities on the specified
259 port. State indicates the new state (defined by
260 enum uart_pm_state), oldstate indicates the previous state.
261
262 This function should not be used to grab any resources.
263
264 This will be called when the port is initially opened and finally
265 closed, except when the port is also the system console. This
266 will occur even if CONFIG_PM is not set.
267
268 Locking: none.
269 Interrupts: caller dependent.
270
271 type(port)
272 Return a pointer to a string constant describing the specified
273 port, or return NULL, in which case the string 'unknown' is
274 substituted.
275
276 Locking: none.
277 Interrupts: caller dependent.
278
279 release_port(port)
280 Release any memory and IO region resources currently in use by
281 the port.
282
283 Locking: none.
284 Interrupts: caller dependent.
285
286 request_port(port)
287 Request any memory and IO region resources required by the port.
288 If any fail, no resources should be registered when this function
289 returns, and it should return -EBUSY on failure.
290
291 Locking: none.
292 Interrupts: caller dependent.
293
294 config_port(port,type)
295 Perform any autoconfiguration steps required for the port. `type`
296 contains a bit mask of the required configuration. UART_CONFIG_TYPE
297 indicates that the port requires detection and identification.
298 port->type should be set to the type found, or PORT_UNKNOWN if
299 no port was detected.
300
301 UART_CONFIG_IRQ indicates autoconfiguration of the interrupt signal,
302 which should be probed using standard kernel autoprobing techniques.
303 This is not necessary on platforms where ports have interrupts
304 internally hard wired (eg, system on a chip implementations).
305
306 Locking: none.
307 Interrupts: caller dependent.
308
309 verify_port(port,serinfo)
310 Verify the new serial port information contained within serinfo is
311 suitable for this port type.
312
313 Locking: none.
314 Interrupts: caller dependent.
315
316 ioctl(port,cmd,arg)
317 Perform any port specific IOCTLs. IOCTL commands must be defined
318 using the standard numbering system found in <asm/ioctl.h>
319
320 Locking: none.
321 Interrupts: caller dependent.
322
323 poll_init(port)
324 Called by kgdb to perform the minimal hardware initialization needed
325 to support poll_put_char() and poll_get_char(). Unlike ->startup()
326 this should not request interrupts.
327
328 Locking: tty_mutex and tty_port->mutex taken.
329 Interrupts: n/a.
330
331 poll_put_char(port,ch)
332 Called by kgdb to write a single character directly to the serial
333 port. It can and should block until there is space in the TX FIFO.
334
335 Locking: none.
336 Interrupts: caller dependent.
337 This call must not sleep
338
339 poll_get_char(port)
340 Called by kgdb to read a single character directly from the serial
341 port. If data is available, it should be returned; otherwise
342 the function should return NO_POLL_CHAR immediately.
343
344 Locking: none.
345 Interrupts: caller dependent.
346 This call must not sleep
347
348Other functions
349---------------
350
351uart_update_timeout(port,cflag,baud)
352 Update the FIFO drain timeout, port->timeout, according to the
353 number of bits, parity, stop bits and baud rate.
354
355 Locking: caller is expected to take port->lock
356 Interrupts: n/a
357
358uart_get_baud_rate(port,termios,old,min,max)
359 Return the numeric baud rate for the specified termios, taking
360 account of the special 38400 baud "kludge". The B0 baud rate
361 is mapped to 9600 baud.
362
363 If the baud rate is not within min..max, then if old is non-NULL,
364 the original baud rate will be tried. If that exceeds the
365 min..max constraint, 9600 baud will be returned. termios will
366 be updated to the baud rate in use.
367
368 Note: min..max must always allow 9600 baud to be selected.
369
370 Locking: caller dependent.
371 Interrupts: n/a
372
373uart_get_divisor(port,baud)
374 Return the divsor (baud_base / baud) for the specified baud
375 rate, appropriately rounded.
376
377 If 38400 baud and custom divisor is selected, return the
378 custom divisor instead.
379
380 Locking: caller dependent.
381 Interrupts: n/a
382
383uart_match_port(port1,port2)
384 This utility function can be used to determine whether two
385 uart_port structures describe the same port.
386
387 Locking: n/a
388 Interrupts: n/a
389
390uart_write_wakeup(port)
391 A driver is expected to call this function when the number of
392 characters in the transmit buffer have dropped below a threshold.
393
394 Locking: port->lock should be held.
395 Interrupts: n/a
396
397uart_register_driver(drv)
398 Register a uart driver with the core driver. We in turn register
399 with the tty layer, and initialise the core driver per-port state.
400
401 drv->port should be NULL, and the per-port structures should be
402 registered using uart_add_one_port after this call has succeeded.
403
404 Locking: none
405 Interrupts: enabled
406
407uart_unregister_driver()
408 Remove all references to a driver from the core driver. The low
409 level driver must have removed all its ports via the
410 uart_remove_one_port() if it registered them with uart_add_one_port().
411
412 Locking: none
413 Interrupts: enabled
414
415uart_suspend_port()
416
417uart_resume_port()
418
419uart_add_one_port()
420
421uart_remove_one_port()
422
423Other notes
424-----------
425
426It is intended some day to drop the 'unused' entries from uart_port, and
427allow low level drivers to register their own individual uart_port's with
428the core. This will allow drivers to use uart_port as a pointer to a
429structure containing both the uart_port entry with their own extensions,
430thus:
431
432 struct my_port {
433 struct uart_port port;
434 int my_stuff;
435 };
436
437Modem control lines via GPIO
438----------------------------
439
440Some helpers are provided in order to set/get modem control lines via GPIO.
441
442mctrl_gpio_init(port, idx):
443 This will get the {cts,rts,...}-gpios from device tree if they are
444 present and request them, set direction etc, and return an
445 allocated structure. devm_* functions are used, so there's no need
446 to call mctrl_gpio_free().
447 As this sets up the irq handling make sure to not handle changes to the
448 gpio input lines in your driver, too.
449
450mctrl_gpio_free(dev, gpios):
451 This will free the requested gpios in mctrl_gpio_init().
452 As devm_* function are used, there's generally no need to call
453 this function.
454
455mctrl_gpio_to_gpiod(gpios, gidx)
456 This returns the gpio structure associated to the modem line index.
457
458mctrl_gpio_set(gpios, mctrl):
459 This will sets the gpios according to the mctrl state.
460
461mctrl_gpio_get(gpios, mctrl):
462 This will update mctrl with the gpios values.
463
464mctrl_gpio_enable_ms(gpios):
465 Enables irqs and handling of changes to the ms lines.
466
467mctrl_gpio_disable_ms(gpios):
468 Disables irqs and handling of changes to the ms lines.