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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.
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.
91 - TIOCM_LOOP Set the port into loopback mode.
92 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
113 Locking: port->lock taken.
114 Interrupts: locally disabled.
115 This call must not sleep
116
117 stop_tx(port)
118 Stop transmitting characters. This might be due to the CTS
119 line becoming inactive or the tty layer indicating we want
120 to stop transmission due to an XOFF character.
121
122 The driver should stop transmitting characters as soon as
123 possible.
124
125 Locking: port->lock taken.
126 Interrupts: locally disabled.
127 This call must not sleep
128
129 start_tx(port)
130 Start transmitting characters.
131
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
147 This method may be called multiple times. Modem status
148 interrupts should be disabled when the shutdown method is
149 called.
150
151 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
170 This method will only be called when the port is initially opened.
171
172 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
181 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
186 Locking: port_sem taken.
187 Interrupts: caller dependent.
188
189 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
200 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
228 n/a 0 n/a character received, marked as
229 TTY_NORMAL
230 None 1 n/a character received, marked as
231 TTY_NORMAL
232 Yes 1 0 character received, marked as
233 TTY_PARITY
234 Yes 1 1 character discarded
235
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
313uart_update_timeout(port,cflag,baud)
314 Update the FIFO drain timeout, port->timeout, according to the
315 number of bits, parity, stop bits and baud rate.
316
317 Locking: caller is expected to take port->lock
318 Interrupts: n/a
319
320uart_get_baud_rate(port,termios,old,min,max)
321 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
325 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
332 Locking: caller dependent.
333 Interrupts: n/a
334
335uart_get_divisor(port,baud)
336 Return the divsor (baud_base / baud) for the specified baud
337 rate, appropriately rounded.
338
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
345uart_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
385Other 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 };
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.