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Commit | Line | Data |
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1da177e4 LT |
1 | |
2 | Low Level Serial API | |
3 | -------------------- | |
4 | ||
5 | ||
1da177e4 LT |
6 | This document is meant as a brief overview of some aspects of the new serial |
7 | driver. It is not complete, any questions you have should be directed to | |
8 | <rmk@arm.linux.org.uk> | |
9 | ||
67ab7f59 | 10 | The reference implementation is contained within amba_pl011.c. |
1da177e4 LT |
11 | |
12 | ||
13 | ||
14 | Low Level Serial Hardware Driver | |
15 | -------------------------------- | |
16 | ||
17 | The low level serial hardware driver is responsible for supplying port | |
18 | information (defined by uart_port) and a set of control methods (defined | |
19 | by uart_ops) to the core serial driver. The low level driver is also | |
20 | responsible for handling interrupts for the port, and providing any | |
21 | console support. | |
22 | ||
23 | ||
24 | Console Support | |
25 | --------------- | |
26 | ||
27 | The serial core provides a few helper functions. This includes identifing | |
28 | the correct port structure (via uart_get_console) and decoding command line | |
29 | arguments (uart_parse_options). | |
30 | ||
d124fd3b GU |
31 | There is also a helper function (uart_console_write) which performs a |
32 | character by character write, translating newlines to CRLF sequences. | |
33 | Driver writers are recommended to use this function rather than implementing | |
34 | their own version. | |
35 | ||
1da177e4 LT |
36 | |
37 | Locking | |
38 | ------- | |
39 | ||
40 | It is the responsibility of the low level hardware driver to perform the | |
41 | necessary locking using port->lock. There are some exceptions (which | |
42 | are described in the uart_ops listing below.) | |
43 | ||
4895b1d7 | 44 | There are two locks. A per-port spinlock, and an overall semaphore. |
1da177e4 LT |
45 | |
46 | From the core driver perspective, the port->lock locks the following | |
47 | data: | |
48 | ||
49 | port->mctrl | |
50 | port->icount | |
b79ef07d GU |
51 | port->state->xmit.head (circ_buf->head) |
52 | port->state->xmit.tail (circ_buf->tail) | |
1da177e4 LT |
53 | |
54 | The low level driver is free to use this lock to provide any additional | |
55 | locking. | |
56 | ||
1da177e4 | 57 | The port_sem semaphore is used to protect against ports being added/ |
7c8ab967 PH |
58 | removed or reconfigured at inappropriate times. Since v2.6.27, this |
59 | semaphore has been the 'mutex' member of the tty_port struct, and | |
95f981f2 | 60 | commonly referred to as the port mutex. |
1da177e4 LT |
61 | |
62 | ||
63 | uart_ops | |
64 | -------- | |
65 | ||
66 | The uart_ops structure is the main interface between serial_core and the | |
67 | hardware specific driver. It contains all the methods to control the | |
68 | hardware. | |
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. | |
67ab7f59 | 89 | - TIOCM_LOOP Set the port into loopback mode. |
1da177e4 LT |
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: | |
343fe407 | 102 | - TIOCM_CAR state of DCD signal |
1da177e4 LT |
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 | ||
c5f4644e RK |
111 | Locking: port->lock taken. |
112 | Interrupts: locally disabled. | |
1da177e4 LT |
113 | This call must not sleep |
114 | ||
b129a8cc | 115 | stop_tx(port) |
1da177e4 LT |
116 | Stop transmitting characters. This might be due to the CTS |
117 | line becoming inactive or the tty layer indicating we want | |
b129a8cc | 118 | to stop transmission due to an XOFF character. |
1da177e4 | 119 | |
6a8f8d72 RK |
120 | The driver should stop transmitting characters as soon as |
121 | possible. | |
122 | ||
1da177e4 LT |
123 | Locking: port->lock taken. |
124 | Interrupts: locally disabled. | |
125 | This call must not sleep | |
126 | ||
b129a8cc | 127 | start_tx(port) |
6a8f8d72 | 128 | Start transmitting characters. |
1da177e4 LT |
129 | |
130 | Locking: port->lock taken. | |
131 | Interrupts: locally disabled. | |
132 | This call must not sleep | |
133 | ||
39c5144e GU |
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. | |
a3bedc3b | 138 | This will be called only if hardware assisted flow control is enabled. |
39c5144e | 139 | |
18717b06 GU |
140 | Locking: serialized with .unthrottle() and termios modification by the |
141 | tty layer. | |
39c5144e | 142 | |
e27585c7 GU |
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. | |
a3bedc3b | 147 | This will be called only if hardware assisted flow control is enabled. |
e27585c7 | 148 | |
18717b06 GU |
149 | Locking: serialized with .throttle() and termios modification by the |
150 | tty layer. | |
e27585c7 | 151 | |
e759d7c5 KC |
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 | ||
db106df3 PH |
159 | Do not transmit if ch == '\0' (__DISABLED_CHAR). |
160 | ||
e759d7c5 KC |
161 | Locking: none. |
162 | Interrupts: caller dependent. | |
163 | ||
1da177e4 LT |
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 | ||
67ab7f59 RK |
175 | This method may be called multiple times. Modem status |
176 | interrupts should be disabled when the shutdown method is | |
177 | called. | |
178 | ||
1da177e4 LT |
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 | ||
95f981f2 | 189 | Locking: caller holds tty_port->mutex |
1da177e4 LT |
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 | ||
67ab7f59 RK |
196 | This method will only be called when the port is initially opened. |
197 | ||
1da177e4 LT |
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 | ||
b79ef07d | 207 | Drivers must not access port->state once this call has completed. |
67ab7f59 RK |
208 | |
209 | This method will only be called when there are no more users of | |
210 | this port. | |
211 | ||
1da177e4 LT |
212 | Locking: port_sem taken. |
213 | Interrupts: caller dependent. | |
214 | ||
6bb0e3a5 HS |
215 | flush_buffer(port) |
216 | Flush any write buffers, reset any DMA state and stop any | |
217 | ongoing DMA transfers. | |
218 | ||
b79ef07d | 219 | This will be called whenever the port->state->xmit circular |
6bb0e3a5 HS |
220 | buffer is cleared. |
221 | ||
222 | Locking: port->lock taken. | |
223 | Interrupts: locally disabled. | |
224 | This call must not sleep | |
225 | ||
1da177e4 LT |
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 | |
89f3da3e | 254 | n/a 0 n/a character received, marked as |
1da177e4 | 255 | TTY_NORMAL |
89f3da3e PK |
256 | None 1 n/a character received, marked as |
257 | TTY_NORMAL | |
258 | Yes 1 0 character received, marked as | |
1da177e4 | 259 | TTY_PARITY |
89f3da3e | 260 | Yes 1 1 character discarded |
1da177e4 LT |
261 | |
262 | Other flags may be used (eg, xon/xoff characters) if your | |
263 | hardware supports hardware "soft" flow control. | |
264 | ||
95f981f2 | 265 | Locking: caller holds tty_port->mutex |
1da177e4 LT |
266 | Interrupts: caller dependent. |
267 | This call must not sleep | |
268 | ||
0adc301e GU |
269 | set_ldisc(port,termios) |
270 | Notifier for discipline change. See Documentation/serial/tty.txt. | |
271 | ||
95f981f2 | 272 | Locking: caller holds tty_port->mutex |
0adc301e | 273 | |
1da177e4 LT |
274 | pm(port,state,oldstate) |
275 | Perform any power management related activities on the specified | |
6f538fe3 LW |
276 | port. State indicates the new state (defined by |
277 | enum uart_pm_state), oldstate indicates the previous state. | |
1da177e4 LT |
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 | ||
e759d7c5 KC |
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 | ||
1da177e4 LT |
365 | Other functions |
366 | --------------- | |
367 | ||
6a8f8d72 | 368 | uart_update_timeout(port,cflag,baud) |
1da177e4 | 369 | Update the FIFO drain timeout, port->timeout, according to the |
6a8f8d72 | 370 | number of bits, parity, stop bits and baud rate. |
1da177e4 LT |
371 | |
372 | Locking: caller is expected to take port->lock | |
373 | Interrupts: n/a | |
374 | ||
6a8f8d72 | 375 | uart_get_baud_rate(port,termios,old,min,max) |
1da177e4 LT |
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 | ||
6a8f8d72 RK |
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 | ||
1da177e4 LT |
387 | Locking: caller dependent. |
388 | Interrupts: n/a | |
389 | ||
6a8f8d72 | 390 | uart_get_divisor(port,baud) |
93a2f632 | 391 | Return the divisor (baud_base / baud) for the specified baud |
6a8f8d72 | 392 | rate, appropriately rounded. |
1da177e4 LT |
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 | ||
6a8f8d72 RK |
400 | uart_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 | ||
407 | uart_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 | ||
414 | uart_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 | ||
424 | uart_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 | ||
432 | uart_suspend_port() | |
433 | ||
434 | uart_resume_port() | |
435 | ||
436 | uart_add_one_port() | |
437 | ||
438 | uart_remove_one_port() | |
439 | ||
1da177e4 LT |
440 | Other notes |
441 | ----------- | |
442 | ||
443 | It is intended some day to drop the 'unused' entries from uart_port, and | |
444 | allow low level drivers to register their own individual uart_port's with | |
445 | the core. This will allow drivers to use uart_port as a pointer to a | |
446 | structure containing both the uart_port entry with their own extensions, | |
447 | thus: | |
448 | ||
449 | struct my_port { | |
450 | struct uart_port port; | |
451 | int my_stuff; | |
452 | }; | |
84130aac RG |
453 | |
454 | Modem control lines via GPIO | |
455 | ---------------------------- | |
456 | ||
457 | Some helpers are provided in order to set/get modem control lines via GPIO. | |
458 | ||
ce59e48f | 459 | mctrl_gpio_init(port, idx): |
84130aac RG |
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(). | |
ce59e48f UKK |
464 | As this sets up the irq handling make sure to not handle changes to the |
465 | gpio input lines in your driver, too. | |
84130aac RG |
466 | |
467 | mctrl_gpio_free(dev, gpios): | |
468 | This will free the requested gpios in mctrl_gpio_init(). | |
d886e7ce | 469 | As devm_* functions are used, there's generally no need to call |
84130aac RG |
470 | this function. |
471 | ||
472 | mctrl_gpio_to_gpiod(gpios, gidx) | |
4817ebb1 GU |
473 | This returns the gpio_desc structure associated to the modem line |
474 | index. | |
84130aac RG |
475 | |
476 | mctrl_gpio_set(gpios, mctrl): | |
477 | This will sets the gpios according to the mctrl state. | |
478 | ||
479 | mctrl_gpio_get(gpios, mctrl): | |
480 | This will update mctrl with the gpios values. | |
ce59e48f UKK |
481 | |
482 | mctrl_gpio_enable_ms(gpios): | |
483 | Enables irqs and handling of changes to the ms lines. | |
484 | ||
485 | mctrl_gpio_disable_ms(gpios): | |
486 | Disables irqs and handling of changes to the ms lines. |