tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2.. c:namespace:: CEC
3
4.. _CEC_TRANSMIT:
5.. _CEC_RECEIVE:
6
7***********************************
8ioctls CEC_RECEIVE and CEC_TRANSMIT
9***********************************
10
11Name
12====
13
14CEC_RECEIVE, CEC_TRANSMIT - Receive or transmit a CEC message
15
16Synopsis
17========
18
19.. c:macro:: CEC_RECEIVE
20
21``int ioctl(int fd, CEC_RECEIVE, struct cec_msg *argp)``
22
23.. c:macro:: CEC_TRANSMIT
24
25``int ioctl(int fd, CEC_TRANSMIT, struct cec_msg *argp)``
26
27Arguments
28=========
29
30``fd``
31 File descriptor returned by :c:func:`open()`.
32
33``argp``
34 Pointer to struct cec_msg.
35
36Description
37===========
38
39To receive a CEC message the application has to fill in the
40``timeout`` field of struct :c:type:`cec_msg` and pass it to
41:ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
42If the file descriptor is in non-blocking mode and there are no received
43messages pending, then it will return -1 and set errno to the ``EAGAIN``
44error code. If the file descriptor is in blocking mode and ``timeout``
45is non-zero and no message arrived within ``timeout`` milliseconds, then
46it will return -1 and set errno to the ``ETIMEDOUT`` error code.
47
48A received message can be:
49
501. a message received from another CEC device (the ``sequence`` field will
51 be 0, ``tx_status`` will be 0 and ``rx_status`` will be non-zero).
522. the transmit result of an earlier non-blocking transmit (the ``sequence``
53 field will be non-zero, ``tx_status`` will be non-zero and ``rx_status``
54 will be 0).
553. the reply to an earlier non-blocking transmit (the ``sequence`` field will
56 be non-zero, ``tx_status`` will be 0 and ``rx_status`` will be non-zero).
57
58To send a CEC message the application has to fill in the struct
59:c:type:`cec_msg` and pass it to :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`.
60The :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` is only available if
61``CEC_CAP_TRANSMIT`` is set. If there is no more room in the transmit
62queue, then it will return -1 and set errno to the ``EBUSY`` error code.
63The transmit queue has enough room for 18 messages (about 1 second worth
64of 2-byte messages). Note that the CEC kernel framework will also reply
65to core messages (see :ref:`cec-core-processing`), so it is not a good
66idea to fully fill up the transmit queue.
67
68If the file descriptor is in non-blocking mode then the transmit will
69return 0 and the result of the transmit will be available via
70:ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>` once the transmit has finished.
71If a non-blocking transmit also specified waiting for a reply, then
72the reply will arrive in a later message. The ``sequence`` field can
73be used to associate both transmit results and replies with the original
74transmit.
75
76Normally calling :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` when the physical
77address is invalid (due to e.g. a disconnect) will return ``ENONET``.
78
79However, the CEC specification allows sending messages from 'Unregistered' to
80'TV' when the physical address is invalid since some TVs pull the hotplug detect
81pin of the HDMI connector low when they go into standby, or when switching to
82another input.
83
84When the hotplug detect pin goes low the EDID disappears, and thus the
85physical address, but the cable is still connected and CEC still works.
86In order to detect/wake up the device it is allowed to send poll and 'Image/Text
87View On' messages from initiator 0xf ('Unregistered') to destination 0 ('TV').
88
89.. tabularcolumns:: |p{1.0cm}|p{3.5cm}|p{12.8cm}|
90
91.. c:type:: cec_msg
92
93.. cssclass:: longtable
94
95.. flat-table:: struct cec_msg
96 :header-rows: 0
97 :stub-columns: 0
98 :widths: 1 1 16
99
100 * - __u64
101 - ``tx_ts``
102 - Timestamp in ns of when the last byte of the message was transmitted.
103 The timestamp has been taken from the ``CLOCK_MONOTONIC`` clock. To access
104 the same clock from userspace use :c:func:`clock_gettime`.
105 * - __u64
106 - ``rx_ts``
107 - Timestamp in ns of when the last byte of the message was received.
108 The timestamp has been taken from the ``CLOCK_MONOTONIC`` clock. To access
109 the same clock from userspace use :c:func:`clock_gettime`.
110 * - __u32
111 - ``len``
112 - The length of the message. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` this is filled in
113 by the application. The driver will fill this in for
114 :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` it will be
115 filled in by the driver with the length of the reply message if ``reply`` was set.
116 * - __u32
117 - ``timeout``
118 - The timeout in milliseconds. This is the time the device will wait
119 for a message to be received before timing out. If it is set to 0,
120 then it will wait indefinitely when it is called by :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
121 If it is 0 and it is called by :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`,
122 then it will be replaced by 1000 if the ``reply`` is non-zero or
123 ignored if ``reply`` is 0.
124 * - __u32
125 - ``sequence``
126 - A non-zero sequence number is automatically assigned by the CEC framework
127 for all transmitted messages. It is used by the CEC framework when it queues
128 the transmit result for a non-blocking transmit. This allows the application
129 to associate the received message with the original transmit.
130
131 In addition, if a non-blocking transmit will wait for a reply (ii.e. ``timeout``
132 was not 0), then the ``sequence`` field of the reply will be set to the sequence
133 value of the original transmit. This allows the application to associate the
134 received message with the original transmit.
135 * - __u32
136 - ``flags``
137 - Flags. See :ref:`cec-msg-flags` for a list of available flags.
138 * - __u8
139 - ``msg[16]``
140 - The message payload. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` this is filled in by the
141 application. The driver will fill this in for :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
142 For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` it will be filled in by the driver with
143 the payload of the reply message if ``timeout`` was set.
144 * - __u8
145 - ``reply``
146 - Wait until this message is replied. If ``reply`` is 0 and the
147 ``timeout`` is 0, then don't wait for a reply but return after
148 transmitting the message. Ignored by :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
149 The case where ``reply`` is 0 (this is the opcode for the Feature Abort
150 message) and ``timeout`` is non-zero is specifically allowed to make it
151 possible to send a message and wait up to ``timeout`` milliseconds for a
152 Feature Abort reply. In this case ``rx_status`` will either be set
153 to :ref:`CEC_RX_STATUS_TIMEOUT <CEC-RX-STATUS-TIMEOUT>` or
154 :ref:`CEC_RX_STATUS_FEATURE_ABORT <CEC-RX-STATUS-FEATURE-ABORT>`.
155
156 If the transmitter message is ``CEC_MSG_INITIATE_ARC`` then the ``reply``
157 values ``CEC_MSG_REPORT_ARC_INITIATED`` and ``CEC_MSG_REPORT_ARC_TERMINATED``
158 are processed differently: either value will match both possible replies.
159 The reason is that the ``CEC_MSG_INITIATE_ARC`` message is the only CEC
160 message that has two possible replies other than Feature Abort. The
161 ``reply`` field will be updated with the actual reply so that it is
162 synchronized with the contents of the received message.
163 * - __u8
164 - ``rx_status``
165 - The status bits of the received message. See
166 :ref:`cec-rx-status` for the possible status values.
167 * - __u8
168 - ``tx_status``
169 - The status bits of the transmitted message. See
170 :ref:`cec-tx-status` for the possible status values.
171 When calling :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` in non-blocking mode,
172 this field will be 0 if the transmit started, or non-0 if the transmit
173 result is known immediately. The latter would be the case when attempting
174 to transmit a Poll message to yourself. That results in a
175 :ref:`CEC_TX_STATUS_NACK <CEC-TX-STATUS-NACK>` without ever actually
176 transmitting the Poll message.
177 * - __u8
178 - ``tx_arb_lost_cnt``
179 - A counter of the number of transmit attempts that resulted in the
180 Arbitration Lost error. This is only set if the hardware supports
181 this, otherwise it is always 0. This counter is only valid if the
182 :ref:`CEC_TX_STATUS_ARB_LOST <CEC-TX-STATUS-ARB-LOST>` status bit is set.
183 * - __u8
184 - ``tx_nack_cnt``
185 - A counter of the number of transmit attempts that resulted in the
186 Not Acknowledged error. This is only set if the hardware supports
187 this, otherwise it is always 0. This counter is only valid if the
188 :ref:`CEC_TX_STATUS_NACK <CEC-TX-STATUS-NACK>` status bit is set.
189 * - __u8
190 - ``tx_low_drive_cnt``
191 - A counter of the number of transmit attempts that resulted in the
192 Arbitration Lost error. This is only set if the hardware supports
193 this, otherwise it is always 0. This counter is only valid if the
194 :ref:`CEC_TX_STATUS_LOW_DRIVE <CEC-TX-STATUS-LOW-DRIVE>` status bit is set.
195 * - __u8
196 - ``tx_error_cnt``
197 - A counter of the number of transmit errors other than Arbitration
198 Lost or Not Acknowledged. This is only set if the hardware
199 supports this, otherwise it is always 0. This counter is only
200 valid if the :ref:`CEC_TX_STATUS_ERROR <CEC-TX-STATUS-ERROR>` status bit is set.
201
202.. tabularcolumns:: |p{6.2cm}|p{1.0cm}|p{10.1cm}|
203
204.. _cec-msg-flags:
205
206.. flat-table:: Flags for struct cec_msg
207 :header-rows: 0
208 :stub-columns: 0
209 :widths: 3 1 4
210
211 * .. _`CEC-MSG-FL-REPLY-TO-FOLLOWERS`:
212
213 - ``CEC_MSG_FL_REPLY_TO_FOLLOWERS``
214 - 1
215 - If a CEC transmit expects a reply, then by default that reply is only sent to
216 the filehandle that called :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`. If this
217 flag is set, then the reply is also sent to all followers, if any. If the
218 filehandle that called :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` is also a
219 follower, then that filehandle will receive the reply twice: once as the
220 result of the :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`, and once via
221 :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
222
223 * .. _`CEC-MSG-FL-RAW`:
224
225 - ``CEC_MSG_FL_RAW``
226 - 2
227 - Normally CEC messages are validated before transmitting them. If this
228 flag is set when :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` is called,
229 then no validation takes place and the message is transmitted as-is.
230 This is useful when debugging CEC issues.
231 This flag is only allowed if the process has the ``CAP_SYS_RAWIO``
232 capability. If that is not set, then the ``EPERM`` error code is
233 returned.
234
235.. tabularcolumns:: |p{5.6cm}|p{0.9cm}|p{10.8cm}|
236
237.. _cec-tx-status:
238
239.. flat-table:: CEC Transmit Status
240 :header-rows: 0
241 :stub-columns: 0
242 :widths: 3 1 16
243
244 * .. _`CEC-TX-STATUS-OK`:
245
246 - ``CEC_TX_STATUS_OK``
247 - 0x01
248 - The message was transmitted successfully. This is mutually
249 exclusive with :ref:`CEC_TX_STATUS_MAX_RETRIES <CEC-TX-STATUS-MAX-RETRIES>`.
250 Other bits can still be set if earlier attempts met with failure before
251 the transmit was eventually successful.
252 * .. _`CEC-TX-STATUS-ARB-LOST`:
253
254 - ``CEC_TX_STATUS_ARB_LOST``
255 - 0x02
256 - CEC line arbitration was lost, i.e. another transmit started at the
257 same time with a higher priority. Optional status, not all hardware
258 can detect this error condition.
259 * .. _`CEC-TX-STATUS-NACK`:
260
261 - ``CEC_TX_STATUS_NACK``
262 - 0x04
263 - Message was not acknowledged. Note that some hardware cannot tell apart
264 a 'Not Acknowledged' status from other error conditions, i.e. the result
265 of a transmit is just OK or FAIL. In that case this status will be
266 returned when the transmit failed.
267 * .. _`CEC-TX-STATUS-LOW-DRIVE`:
268
269 - ``CEC_TX_STATUS_LOW_DRIVE``
270 - 0x08
271 - Low drive was detected on the CEC bus. This indicates that a
272 follower detected an error on the bus and requests a
273 retransmission. Optional status, not all hardware can detect this
274 error condition.
275 * .. _`CEC-TX-STATUS-ERROR`:
276
277 - ``CEC_TX_STATUS_ERROR``
278 - 0x10
279 - Some error occurred. This is used for any errors that do not fit
280 ``CEC_TX_STATUS_ARB_LOST`` or ``CEC_TX_STATUS_LOW_DRIVE``, either because
281 the hardware could not tell which error occurred, or because the hardware
282 tested for other conditions besides those two. Optional status.
283 * .. _`CEC-TX-STATUS-MAX-RETRIES`:
284
285 - ``CEC_TX_STATUS_MAX_RETRIES``
286 - 0x20
287 - The transmit failed after one or more retries. This status bit is
288 mutually exclusive with :ref:`CEC_TX_STATUS_OK <CEC-TX-STATUS-OK>`.
289 Other bits can still be set to explain which failures were seen.
290 * .. _`CEC-TX-STATUS-ABORTED`:
291
292 - ``CEC_TX_STATUS_ABORTED``
293 - 0x40
294 - The transmit was aborted due to an HDMI disconnect, or the adapter
295 was unconfigured, or a transmit was interrupted, or the driver
296 returned an error when attempting to start a transmit.
297 * .. _`CEC-TX-STATUS-TIMEOUT`:
298
299 - ``CEC_TX_STATUS_TIMEOUT``
300 - 0x80
301 - The transmit timed out. This should not normally happen and this
302 indicates a driver problem.
303
304.. tabularcolumns:: |p{5.6cm}|p{0.9cm}|p{10.8cm}|
305
306.. _cec-rx-status:
307
308.. flat-table:: CEC Receive Status
309 :header-rows: 0
310 :stub-columns: 0
311 :widths: 3 1 16
312
313 * .. _`CEC-RX-STATUS-OK`:
314
315 - ``CEC_RX_STATUS_OK``
316 - 0x01
317 - The message was received successfully.
318 * .. _`CEC-RX-STATUS-TIMEOUT`:
319
320 - ``CEC_RX_STATUS_TIMEOUT``
321 - 0x02
322 - The reply to an earlier transmitted message timed out.
323 * .. _`CEC-RX-STATUS-FEATURE-ABORT`:
324
325 - ``CEC_RX_STATUS_FEATURE_ABORT``
326 - 0x04
327 - The message was received successfully but the reply was
328 ``CEC_MSG_FEATURE_ABORT``. This status is only set if this message
329 was the reply to an earlier transmitted message.
330 * .. _`CEC-RX-STATUS-ABORTED`:
331
332 - ``CEC_RX_STATUS_ABORTED``
333 - 0x08
334 - The wait for a reply to an earlier transmitted message was aborted
335 because the HDMI cable was disconnected, the adapter was unconfigured
336 or the :ref:`CEC_TRANSMIT <CEC_RECEIVE>` that waited for a
337 reply was interrupted.
338
339
340Return Value
341============
342
343On success 0 is returned, on error -1 and the ``errno`` variable is set
344appropriately. The generic error codes are described at the
345:ref:`Generic Error Codes <gen-errors>` chapter.
346
347The :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>` can return the following
348error codes:
349
350EAGAIN
351 No messages are in the receive queue, and the filehandle is in non-blocking mode.
352
353ETIMEDOUT
354 The ``timeout`` was reached while waiting for a message.
355
356ERESTARTSYS
357 The wait for a message was interrupted (e.g. by Ctrl-C).
358
359The :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` can return the following
360error codes:
361
362ENOTTY
363 The ``CEC_CAP_TRANSMIT`` capability wasn't set, so this ioctl is not supported.
364
365EPERM
366 The CEC adapter is not configured, i.e. :ref:`ioctl CEC_ADAP_S_LOG_ADDRS <CEC_ADAP_S_LOG_ADDRS>`
367 has never been called, or ``CEC_MSG_FL_RAW`` was used from a process that
368 did not have the ``CAP_SYS_RAWIO`` capability.
369
370ENONET
371 The CEC adapter is not configured, i.e. :ref:`ioctl CEC_ADAP_S_LOG_ADDRS <CEC_ADAP_S_LOG_ADDRS>`
372 was called, but the physical address is invalid so no logical address was claimed.
373 An exception is made in this case for transmits from initiator 0xf ('Unregistered')
374 to destination 0 ('TV'). In that case the transmit will proceed as usual.
375
376EBUSY
377 Another filehandle is in exclusive follower or initiator mode, or the filehandle
378 is in mode ``CEC_MODE_NO_INITIATOR``. This is also returned if the transmit
379 queue is full.
380
381EINVAL
382 The contents of struct :c:type:`cec_msg` is invalid.
383
384ERESTARTSYS
385 The wait for a successful transmit was interrupted (e.g. by Ctrl-C).