tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
1.. -*- coding: utf-8; mode: rst -*-
2
3.. _CEC_TRANSMIT:
4.. _CEC_RECEIVE:
5
6***********************************
7ioctls CEC_RECEIVE and CEC_TRANSMIT
8***********************************
9
10Name
11====
12
13CEC_RECEIVE, CEC_TRANSMIT - Receive or transmit a CEC message
14
15
16Synopsis
17========
18
19.. c:function:: int ioctl( int fd, CEC_RECEIVE, struct cec_msg *argp )
20 :name: CEC_RECEIVE
21
22.. c:function:: int ioctl( int fd, CEC_TRANSMIT, struct cec_msg *argp )
23 :name: CEC_TRANSMIT
24
25Arguments
26=========
27
28``fd``
29 File descriptor returned by :c:func:`open() <cec-open>`.
30
31``argp``
32 Pointer to struct cec_msg.
33
34Description
35===========
36
37To receive a CEC message the application has to fill in the
38``timeout`` field of struct :c:type:`cec_msg` and pass it to
39:ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
40If the file descriptor is in non-blocking mode and there are no received
41messages pending, then it will return -1 and set errno to the ``EAGAIN``
42error code. If the file descriptor is in blocking mode and ``timeout``
43is non-zero and no message arrived within ``timeout`` milliseconds, then
44it will return -1 and set errno to the ``ETIMEDOUT`` error code.
45
46A received message can be:
47
481. a message received from another CEC device (the ``sequence`` field will
49 be 0).
502. the result of an earlier non-blocking transmit (the ``sequence`` field will
51 be non-zero).
52
53To send a CEC message the application has to fill in the struct
54:c:type:`cec_msg` and pass it to :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`.
55The :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` is only available if
56``CEC_CAP_TRANSMIT`` is set. If there is no more room in the transmit
57queue, then it will return -1 and set errno to the ``EBUSY`` error code.
58The transmit queue has enough room for 18 messages (about 1 second worth
59of 2-byte messages). Note that the CEC kernel framework will also reply
60to core messages (see :ref:`cec-core-processing`), so it is not a good
61idea to fully fill up the transmit queue.
62
63If the file descriptor is in non-blocking mode then the transmit will
64return 0 and the result of the transmit will be available via
65:ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>` once the transmit has finished
66(including waiting for a reply, if requested).
67
68The ``sequence`` field is filled in for every transmit and this can be
69checked against the received messages to find the corresponding transmit
70result.
71
72Normally calling :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` when the physical
73address is invalid (due to e.g. a disconnect) will return ``ENONET``.
74
75However, the CEC specification allows sending messages from 'Unregistered' to
76'TV' when the physical address is invalid since some TVs pull the hotplug detect
77pin of the HDMI connector low when they go into standby, or when switching to
78another input.
79
80When the hotplug detect pin goes low the EDID disappears, and thus the
81physical address, but the cable is still connected and CEC still works.
82In order to detect/wake up the device it is allowed to send poll and 'Image/Text
83View On' messages from initiator 0xf ('Unregistered') to destination 0 ('TV').
84
85.. tabularcolumns:: |p{1.0cm}|p{3.5cm}|p{13.0cm}|
86
87.. c:type:: cec_msg
88
89.. cssclass:: longtable
90
91.. flat-table:: struct cec_msg
92 :header-rows: 0
93 :stub-columns: 0
94 :widths: 1 1 16
95
96 * - __u64
97 - ``tx_ts``
98 - Timestamp in ns of when the last byte of the message was transmitted.
99 The timestamp has been taken from the ``CLOCK_MONOTONIC`` clock. To access
100 the same clock from userspace use :c:func:`clock_gettime`.
101 * - __u64
102 - ``rx_ts``
103 - Timestamp in ns of when the last byte of the message was received.
104 The timestamp has been taken from the ``CLOCK_MONOTONIC`` clock. To access
105 the same clock from userspace use :c:func:`clock_gettime`.
106 * - __u32
107 - ``len``
108 - The length of the message. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` this is filled in
109 by the application. The driver will fill this in for
110 :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` it will be
111 filled in by the driver with the length of the reply message if ``reply`` was set.
112 * - __u32
113 - ``timeout``
114 - The timeout in milliseconds. This is the time the device will wait
115 for a message to be received before timing out. If it is set to 0,
116 then it will wait indefinitely when it is called by :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
117 If it is 0 and it is called by :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`,
118 then it will be replaced by 1000 if the ``reply`` is non-zero or
119 ignored if ``reply`` is 0.
120 * - __u32
121 - ``sequence``
122 - A non-zero sequence number is automatically assigned by the CEC framework
123 for all transmitted messages. It is used by the CEC framework when it queues
124 the transmit result (when transmit was called in non-blocking mode). This
125 allows the application to associate the received message with the original
126 transmit.
127 * - __u32
128 - ``flags``
129 - Flags. See :ref:`cec-msg-flags` for a list of available flags.
130 * - __u8
131 - ``tx_status``
132 - The status bits of the transmitted message. See
133 :ref:`cec-tx-status` for the possible status values. It is 0 if
134 this messages was received, not transmitted.
135 * - __u8
136 - ``msg[16]``
137 - The message payload. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` this is filled in by the
138 application. The driver will fill this in for :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
139 For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` it will be filled in by the driver with
140 the payload of the reply message if ``timeout`` was set.
141 * - __u8
142 - ``reply``
143 - Wait until this message is replied. If ``reply`` is 0 and the
144 ``timeout`` is 0, then don't wait for a reply but return after
145 transmitting the message. Ignored by :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
146 The case where ``reply`` is 0 (this is the opcode for the Feature Abort
147 message) and ``timeout`` is non-zero is specifically allowed to make it
148 possible to send a message and wait up to ``timeout`` milliseconds for a
149 Feature Abort reply. In this case ``rx_status`` will either be set
150 to :ref:`CEC_RX_STATUS_TIMEOUT <CEC-RX-STATUS-TIMEOUT>` or
151 :ref:`CEC_RX_STATUS_FEATURE_ABORT <CEC-RX-STATUS-FEATURE-ABORT>`.
152
153 If the transmitter message is ``CEC_MSG_INITIATE_ARC`` then the ``reply``
154 values ``CEC_MSG_REPORT_ARC_INITIATED`` and ``CEC_MSG_REPORT_ARC_TERMINATED``
155 are processed differently: either value will match both possible replies.
156 The reason is that the ``CEC_MSG_INITIATE_ARC`` message is the only CEC
157 message that has two possible replies other than Feature Abort. The
158 ``reply`` field will be updated with the actual reply so that it is
159 synchronized with the contents of the received message.
160 * - __u8
161 - ``rx_status``
162 - The status bits of the received message. See
163 :ref:`cec-rx-status` for the possible status values. It is 0 if
164 this message was transmitted, not received, unless this is the
165 reply to a transmitted message. In that case both ``rx_status``
166 and ``tx_status`` are set.
167 * - __u8
168 - ``tx_status``
169 - The status bits of the transmitted message. See
170 :ref:`cec-tx-status` for the possible status values. It is 0 if
171 this messages was received, not transmitted.
172 * - __u8
173 - ``tx_arb_lost_cnt``
174 - A counter of the number of transmit attempts that resulted in the
175 Arbitration Lost error. This is only set if the hardware supports
176 this, otherwise it is always 0. This counter is only valid if the
177 :ref:`CEC_TX_STATUS_ARB_LOST <CEC-TX-STATUS-ARB-LOST>` status bit is set.
178 * - __u8
179 - ``tx_nack_cnt``
180 - A counter of the number of transmit attempts that resulted in the
181 Not Acknowledged error. This is only set if the hardware supports
182 this, otherwise it is always 0. This counter is only valid if the
183 :ref:`CEC_TX_STATUS_NACK <CEC-TX-STATUS-NACK>` status bit is set.
184 * - __u8
185 - ``tx_low_drive_cnt``
186 - A counter of the number of transmit attempts that resulted in the
187 Arbitration Lost error. This is only set if the hardware supports
188 this, otherwise it is always 0. This counter is only valid if the
189 :ref:`CEC_TX_STATUS_LOW_DRIVE <CEC-TX-STATUS-LOW-DRIVE>` status bit is set.
190 * - __u8
191 - ``tx_error_cnt``
192 - A counter of the number of transmit errors other than Arbitration
193 Lost or Not Acknowledged. This is only set if the hardware
194 supports this, otherwise it is always 0. This counter is only
195 valid if the :ref:`CEC_TX_STATUS_ERROR <CEC-TX-STATUS-ERROR>` status bit is set.
196
197
198.. _cec-msg-flags:
199
200.. flat-table:: Flags for struct cec_msg
201 :header-rows: 0
202 :stub-columns: 0
203 :widths: 3 1 4
204
205 * .. _`CEC-MSG-FL-REPLY-TO-FOLLOWERS`:
206
207 - ``CEC_MSG_FL_REPLY_TO_FOLLOWERS``
208 - 1
209 - If a CEC transmit expects a reply, then by default that reply is only sent to
210 the filehandle that called :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`. If this
211 flag is set, then the reply is also sent to all followers, if any. If the
212 filehandle that called :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` is also a
213 follower, then that filehandle will receive the reply twice: once as the
214 result of the :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`, and once via
215 :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
216
217
218.. tabularcolumns:: |p{5.6cm}|p{0.9cm}|p{11.0cm}|
219
220.. _cec-tx-status:
221
222.. flat-table:: CEC Transmit Status
223 :header-rows: 0
224 :stub-columns: 0
225 :widths: 3 1 16
226
227 * .. _`CEC-TX-STATUS-OK`:
228
229 - ``CEC_TX_STATUS_OK``
230 - 0x01
231 - The message was transmitted successfully. This is mutually
232 exclusive with :ref:`CEC_TX_STATUS_MAX_RETRIES <CEC-TX-STATUS-MAX-RETRIES>`. Other bits can still
233 be set if earlier attempts met with failure before the transmit
234 was eventually successful.
235 * .. _`CEC-TX-STATUS-ARB-LOST`:
236
237 - ``CEC_TX_STATUS_ARB_LOST``
238 - 0x02
239 - CEC line arbitration was lost.
240 * .. _`CEC-TX-STATUS-NACK`:
241
242 - ``CEC_TX_STATUS_NACK``
243 - 0x04
244 - Message was not acknowledged.
245 * .. _`CEC-TX-STATUS-LOW-DRIVE`:
246
247 - ``CEC_TX_STATUS_LOW_DRIVE``
248 - 0x08
249 - Low drive was detected on the CEC bus. This indicates that a
250 follower detected an error on the bus and requests a
251 retransmission.
252 * .. _`CEC-TX-STATUS-ERROR`:
253
254 - ``CEC_TX_STATUS_ERROR``
255 - 0x10
256 - Some error occurred. This is used for any errors that do not fit
257 the previous two, either because the hardware could not tell which
258 error occurred, or because the hardware tested for other
259 conditions besides those two.
260 * .. _`CEC-TX-STATUS-MAX-RETRIES`:
261
262 - ``CEC_TX_STATUS_MAX_RETRIES``
263 - 0x20
264 - The transmit failed after one or more retries. This status bit is
265 mutually exclusive with :ref:`CEC_TX_STATUS_OK <CEC-TX-STATUS-OK>`. Other bits can still
266 be set to explain which failures were seen.
267
268
269.. tabularcolumns:: |p{5.6cm}|p{0.9cm}|p{11.0cm}|
270
271.. _cec-rx-status:
272
273.. flat-table:: CEC Receive Status
274 :header-rows: 0
275 :stub-columns: 0
276 :widths: 3 1 16
277
278 * .. _`CEC-RX-STATUS-OK`:
279
280 - ``CEC_RX_STATUS_OK``
281 - 0x01
282 - The message was received successfully.
283 * .. _`CEC-RX-STATUS-TIMEOUT`:
284
285 - ``CEC_RX_STATUS_TIMEOUT``
286 - 0x02
287 - The reply to an earlier transmitted message timed out.
288 * .. _`CEC-RX-STATUS-FEATURE-ABORT`:
289
290 - ``CEC_RX_STATUS_FEATURE_ABORT``
291 - 0x04
292 - The message was received successfully but the reply was
293 ``CEC_MSG_FEATURE_ABORT``. This status is only set if this message
294 was the reply to an earlier transmitted message.
295
296
297
298Return Value
299============
300
301On success 0 is returned, on error -1 and the ``errno`` variable is set
302appropriately. The generic error codes are described at the
303:ref:`Generic Error Codes <gen-errors>` chapter.
304
305The :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>` can return the following
306error codes:
307
308EAGAIN
309 No messages are in the receive queue, and the filehandle is in non-blocking mode.
310
311ETIMEDOUT
312 The ``timeout`` was reached while waiting for a message.
313
314ERESTARTSYS
315 The wait for a message was interrupted (e.g. by Ctrl-C).
316
317The :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` can return the following
318error codes:
319
320ENOTTY
321 The ``CEC_CAP_TRANSMIT`` capability wasn't set, so this ioctl is not supported.
322
323EPERM
324 The CEC adapter is not configured, i.e. :ref:`ioctl CEC_ADAP_S_LOG_ADDRS <CEC_ADAP_S_LOG_ADDRS>`
325 has never been called.
326
327ENONET
328 The CEC adapter is not configured, i.e. :ref:`ioctl CEC_ADAP_S_LOG_ADDRS <CEC_ADAP_S_LOG_ADDRS>`
329 was called, but the physical address is invalid so no logical address was claimed.
330 An exception is made in this case for transmits from initiator 0xf ('Unregistered')
331 to destination 0 ('TV'). In that case the transmit will proceed as usual.
332
333EBUSY
334 Another filehandle is in exclusive follower or initiator mode, or the filehandle
335 is in mode ``CEC_MODE_NO_INITIATOR``. This is also returned if the transmit
336 queue is full.
337
338EINVAL
339 The contents of struct :c:type:`cec_msg` is invalid.
340
341ERESTARTSYS
342 The wait for a successful transmit was interrupted (e.g. by Ctrl-C).