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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
37.. note::
38
39 This documents the proposed CEC API. This API is not yet finalized
40 and is currently only available as a staging kernel module.
41
42To receive a CEC message the application has to fill in the
43``timeout`` field of struct :c:type:`cec_msg` and pass it to
44:ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
45If the file descriptor is in non-blocking mode and there are no received
46messages pending, then it will return -1 and set errno to the ``EAGAIN``
47error code. If the file descriptor is in blocking mode and ``timeout``
48is non-zero and no message arrived within ``timeout`` milliseconds, then
49it will return -1 and set errno to the ``ETIMEDOUT`` error code.
50
51A received message can be:
52
531. a message received from another CEC device (the ``sequence`` field will
54 be 0).
552. the result of an earlier non-blocking transmit (the ``sequence`` field will
56 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
71(including waiting for a reply, if requested).
72
73The ``sequence`` field is filled in for every transmit and this can be
74checked against the received messages to find the corresponding transmit
75result.
76
77
78.. tabularcolumns:: |p{1.0cm}|p{3.5cm}|p{13.0cm}|
79
80.. c:type:: cec_msg
81
82.. cssclass:: longtable
83
84.. flat-table:: struct cec_msg
85 :header-rows: 0
86 :stub-columns: 0
87 :widths: 1 1 16
88
89 * - __u64
90 - ``tx_ts``
91 - Timestamp in ns of when the last byte of the message was transmitted.
92 The timestamp has been taken from the ``CLOCK_MONOTONIC`` clock. To access
93 the same clock from userspace use :c:func:`clock_gettime`.
94 * - __u64
95 - ``rx_ts``
96 - Timestamp in ns of when the last byte of the message was received.
97 The timestamp has been taken from the ``CLOCK_MONOTONIC`` clock. To access
98 the same clock from userspace use :c:func:`clock_gettime`.
99 * - __u32
100 - ``len``
101 - The length of the message. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` this is filled in
102 by the application. The driver will fill this in for
103 :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` it will be
104 filled in by the driver with the length of the reply message if ``reply`` was set.
105 * - __u32
106 - ``timeout``
107 - The timeout in milliseconds. This is the time the device will wait
108 for a message to be received before timing out. If it is set to 0,
109 then it will wait indefinitely when it is called by :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
110 If it is 0 and it is called by :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`,
111 then it will be replaced by 1000 if the ``reply`` is non-zero or
112 ignored if ``reply`` is 0.
113 * - __u32
114 - ``sequence``
115 - A non-zero sequence number is automatically assigned by the CEC framework
116 for all transmitted messages. It is used by the CEC framework when it queues
117 the transmit result (when transmit was called in non-blocking mode). This
118 allows the application to associate the received message with the original
119 transmit.
120 * - __u32
121 - ``flags``
122 - Flags. See :ref:`cec-msg-flags` for a list of available flags.
123 * - __u8
124 - ``tx_status``
125 - The status bits of the transmitted message. See
126 :ref:`cec-tx-status` for the possible status values. It is 0 if
127 this messages was received, not transmitted.
128 * - __u8
129 - ``msg[16]``
130 - The message payload. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` this is filled in by the
131 application. The driver will fill this in for :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
132 For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` it will be filled in by the driver with
133 the payload of the reply message if ``timeout`` was set.
134 * - __u8
135 - ``reply``
136 - Wait until this message is replied. If ``reply`` is 0 and the
137 ``timeout`` is 0, then don't wait for a reply but return after
138 transmitting the message. Ignored by :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
139 The case where ``reply`` is 0 (this is the opcode for the Feature Abort
140 message) and ``timeout`` is non-zero is specifically allowed to make it
141 possible to send a message and wait up to ``timeout`` milliseconds for a
142 Feature Abort reply. In this case ``rx_status`` will either be set
143 to :ref:`CEC_RX_STATUS_TIMEOUT <CEC-RX-STATUS-TIMEOUT>` or
144 :ref:`CEC_RX_STATUS_FEATURE_ABORT <CEC-RX-STATUS-FEATURE-ABORT>`.
145
146 If the transmitter message is ``CEC_MSG_INITIATE_ARC`` then the ``reply``
147 values ``CEC_MSG_REPORT_ARC_INITIATED`` and ``CEC_MSG_REPORT_ARC_TERMINATED``
148 are processed differently: either value will match both possible replies.
149 The reason is that the ``CEC_MSG_INITIATE_ARC`` message is the only CEC
150 message that has two possible replies other than Feature Abort. The
151 ``reply`` field will be updated with the actual reply so that it is
152 synchronized with the contents of the received message.
153 * - __u8
154 - ``rx_status``
155 - The status bits of the received message. See
156 :ref:`cec-rx-status` for the possible status values. It is 0 if
157 this message was transmitted, not received, unless this is the
158 reply to a transmitted message. In that case both ``rx_status``
159 and ``tx_status`` are set.
160 * - __u8
161 - ``tx_status``
162 - The status bits of the transmitted message. See
163 :ref:`cec-tx-status` for the possible status values. It is 0 if
164 this messages was received, not transmitted.
165 * - __u8
166 - ``tx_arb_lost_cnt``
167 - A counter of the number of transmit attempts that resulted in the
168 Arbitration Lost error. This is only set if the hardware supports
169 this, otherwise it is always 0. This counter is only valid if the
170 :ref:`CEC_TX_STATUS_ARB_LOST <CEC-TX-STATUS-ARB-LOST>` status bit is set.
171 * - __u8
172 - ``tx_nack_cnt``
173 - A counter of the number of transmit attempts that resulted in the
174 Not Acknowledged error. This is only set if the hardware supports
175 this, otherwise it is always 0. This counter is only valid if the
176 :ref:`CEC_TX_STATUS_NACK <CEC-TX-STATUS-NACK>` status bit is set.
177 * - __u8
178 - ``tx_low_drive_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_LOW_DRIVE <CEC-TX-STATUS-LOW-DRIVE>` status bit is set.
183 * - __u8
184 - ``tx_error_cnt``
185 - A counter of the number of transmit errors other than Arbitration
186 Lost or Not Acknowledged. This is only set if the hardware
187 supports this, otherwise it is always 0. This counter is only
188 valid if the :ref:`CEC_TX_STATUS_ERROR <CEC-TX-STATUS-ERROR>` status bit is set.
189
190
191.. _cec-msg-flags:
192
193.. flat-table:: Flags for struct cec_msg
194 :header-rows: 0
195 :stub-columns: 0
196 :widths: 3 1 4
197
198 * .. _`CEC-MSG-FL-REPLY-TO-FOLLOWERS`:
199
200 - ``CEC_MSG_FL_REPLY_TO_FOLLOWERS``
201 - 1
202 - If a CEC transmit expects a reply, then by default that reply is only sent to
203 the filehandle that called :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`. If this
204 flag is set, then the reply is also sent to all followers, if any. If the
205 filehandle that called :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` is also a
206 follower, then that filehandle will receive the reply twice: once as the
207 result of the :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`, and once via
208 :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
209
210
211.. tabularcolumns:: |p{5.6cm}|p{0.9cm}|p{11.0cm}|
212
213.. _cec-tx-status:
214
215.. flat-table:: CEC Transmit Status
216 :header-rows: 0
217 :stub-columns: 0
218 :widths: 3 1 16
219
220 * .. _`CEC-TX-STATUS-OK`:
221
222 - ``CEC_TX_STATUS_OK``
223 - 0x01
224 - The message was transmitted successfully. This is mutually
225 exclusive with :ref:`CEC_TX_STATUS_MAX_RETRIES <CEC-TX-STATUS-MAX-RETRIES>`. Other bits can still
226 be set if earlier attempts met with failure before the transmit
227 was eventually successful.
228 * .. _`CEC-TX-STATUS-ARB-LOST`:
229
230 - ``CEC_TX_STATUS_ARB_LOST``
231 - 0x02
232 - CEC line arbitration was lost.
233 * .. _`CEC-TX-STATUS-NACK`:
234
235 - ``CEC_TX_STATUS_NACK``
236 - 0x04
237 - Message was not acknowledged.
238 * .. _`CEC-TX-STATUS-LOW-DRIVE`:
239
240 - ``CEC_TX_STATUS_LOW_DRIVE``
241 - 0x08
242 - Low drive was detected on the CEC bus. This indicates that a
243 follower detected an error on the bus and requests a
244 retransmission.
245 * .. _`CEC-TX-STATUS-ERROR`:
246
247 - ``CEC_TX_STATUS_ERROR``
248 - 0x10
249 - Some error occurred. This is used for any errors that do not fit
250 the previous two, either because the hardware could not tell which
251 error occurred, or because the hardware tested for other
252 conditions besides those two.
253 * .. _`CEC-TX-STATUS-MAX-RETRIES`:
254
255 - ``CEC_TX_STATUS_MAX_RETRIES``
256 - 0x20
257 - The transmit failed after one or more retries. This status bit is
258 mutually exclusive with :ref:`CEC_TX_STATUS_OK <CEC-TX-STATUS-OK>`. Other bits can still
259 be set to explain which failures were seen.
260
261
262.. tabularcolumns:: |p{5.6cm}|p{0.9cm}|p{11.0cm}|
263
264.. _cec-rx-status:
265
266.. flat-table:: CEC Receive Status
267 :header-rows: 0
268 :stub-columns: 0
269 :widths: 3 1 16
270
271 * .. _`CEC-RX-STATUS-OK`:
272
273 - ``CEC_RX_STATUS_OK``
274 - 0x01
275 - The message was received successfully.
276 * .. _`CEC-RX-STATUS-TIMEOUT`:
277
278 - ``CEC_RX_STATUS_TIMEOUT``
279 - 0x02
280 - The reply to an earlier transmitted message timed out.
281 * .. _`CEC-RX-STATUS-FEATURE-ABORT`:
282
283 - ``CEC_RX_STATUS_FEATURE_ABORT``
284 - 0x04
285 - The message was received successfully but the reply was
286 ``CEC_MSG_FEATURE_ABORT``. This status is only set if this message
287 was the reply to an earlier transmitted message.
288
289
290
291Return Value
292============
293
294On success 0 is returned, on error -1 and the ``errno`` variable is set
295appropriately. The generic error codes are described at the
296:ref:`Generic Error Codes <gen-errors>` chapter.