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
72
73.. tabularcolumns:: |p{1.0cm}|p{3.5cm}|p{13.0cm}|
74
75.. c:type:: cec_msg
76
77.. cssclass:: longtable
78
79.. flat-table:: struct cec_msg
80 :header-rows: 0
81 :stub-columns: 0
82 :widths: 1 1 16
83
84 * - __u64
85 - ``tx_ts``
86 - Timestamp in ns of when the last byte of the message was transmitted.
87 The timestamp has been taken from the ``CLOCK_MONOTONIC`` clock. To access
88 the same clock from userspace use :c:func:`clock_gettime`.
89 * - __u64
90 - ``rx_ts``
91 - Timestamp in ns of when the last byte of the message was received.
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 * - __u32
95 - ``len``
96 - The length of the message. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` this is filled in
97 by the application. The driver will fill this in for
98 :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` it will be
99 filled in by the driver with the length of the reply message if ``reply`` was set.
100 * - __u32
101 - ``timeout``
102 - The timeout in milliseconds. This is the time the device will wait
103 for a message to be received before timing out. If it is set to 0,
104 then it will wait indefinitely when it is called by :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
105 If it is 0 and it is called by :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`,
106 then it will be replaced by 1000 if the ``reply`` is non-zero or
107 ignored if ``reply`` is 0.
108 * - __u32
109 - ``sequence``
110 - A non-zero sequence number is automatically assigned by the CEC framework
111 for all transmitted messages. It is used by the CEC framework when it queues
112 the transmit result (when transmit was called in non-blocking mode). This
113 allows the application to associate the received message with the original
114 transmit.
115 * - __u32
116 - ``flags``
117 - Flags. See :ref:`cec-msg-flags` for a list of available flags.
118 * - __u8
119 - ``tx_status``
120 - The status bits of the transmitted message. See
121 :ref:`cec-tx-status` for the possible status values. It is 0 if
122 this messages was received, not transmitted.
123 * - __u8
124 - ``msg[16]``
125 - The message payload. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` this is filled in by the
126 application. The driver will fill this in for :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
127 For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` it will be filled in by the driver with
128 the payload of the reply message if ``timeout`` was set.
129 * - __u8
130 - ``reply``
131 - Wait until this message is replied. If ``reply`` is 0 and the
132 ``timeout`` is 0, then don't wait for a reply but return after
133 transmitting the message. Ignored by :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
134 The case where ``reply`` is 0 (this is the opcode for the Feature Abort
135 message) and ``timeout`` is non-zero is specifically allowed to make it
136 possible to send a message and wait up to ``timeout`` milliseconds for a
137 Feature Abort reply. In this case ``rx_status`` will either be set
138 to :ref:`CEC_RX_STATUS_TIMEOUT <CEC-RX-STATUS-TIMEOUT>` or
139 :ref:`CEC_RX_STATUS_FEATURE_ABORT <CEC-RX-STATUS-FEATURE-ABORT>`.
140
141 If the transmitter message is ``CEC_MSG_INITIATE_ARC`` then the ``reply``
142 values ``CEC_MSG_REPORT_ARC_INITIATED`` and ``CEC_MSG_REPORT_ARC_TERMINATED``
143 are processed differently: either value will match both possible replies.
144 The reason is that the ``CEC_MSG_INITIATE_ARC`` message is the only CEC
145 message that has two possible replies other than Feature Abort. The
146 ``reply`` field will be updated with the actual reply so that it is
147 synchronized with the contents of the received message.
148 * - __u8
149 - ``rx_status``
150 - The status bits of the received message. See
151 :ref:`cec-rx-status` for the possible status values. It is 0 if
152 this message was transmitted, not received, unless this is the
153 reply to a transmitted message. In that case both ``rx_status``
154 and ``tx_status`` are set.
155 * - __u8
156 - ``tx_status``
157 - The status bits of the transmitted message. See
158 :ref:`cec-tx-status` for the possible status values. It is 0 if
159 this messages was received, not transmitted.
160 * - __u8
161 - ``tx_arb_lost_cnt``
162 - A counter of the number of transmit attempts that resulted in the
163 Arbitration Lost error. This is only set if the hardware supports
164 this, otherwise it is always 0. This counter is only valid if the
165 :ref:`CEC_TX_STATUS_ARB_LOST <CEC-TX-STATUS-ARB-LOST>` status bit is set.
166 * - __u8
167 - ``tx_nack_cnt``
168 - A counter of the number of transmit attempts that resulted in the
169 Not Acknowledged error. This is only set if the hardware supports
170 this, otherwise it is always 0. This counter is only valid if the
171 :ref:`CEC_TX_STATUS_NACK <CEC-TX-STATUS-NACK>` status bit is set.
172 * - __u8
173 - ``tx_low_drive_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_LOW_DRIVE <CEC-TX-STATUS-LOW-DRIVE>` status bit is set.
178 * - __u8
179 - ``tx_error_cnt``
180 - A counter of the number of transmit errors other than Arbitration
181 Lost or Not Acknowledged. This is only set if the hardware
182 supports this, otherwise it is always 0. This counter is only
183 valid if the :ref:`CEC_TX_STATUS_ERROR <CEC-TX-STATUS-ERROR>` status bit is set.
184
185
186.. _cec-msg-flags:
187
188.. flat-table:: Flags for struct cec_msg
189 :header-rows: 0
190 :stub-columns: 0
191 :widths: 3 1 4
192
193 * .. _`CEC-MSG-FL-REPLY-TO-FOLLOWERS`:
194
195 - ``CEC_MSG_FL_REPLY_TO_FOLLOWERS``
196 - 1
197 - If a CEC transmit expects a reply, then by default that reply is only sent to
198 the filehandle that called :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`. If this
199 flag is set, then the reply is also sent to all followers, if any. If the
200 filehandle that called :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` is also a
201 follower, then that filehandle will receive the reply twice: once as the
202 result of the :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`, and once via
203 :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
204
205
206.. tabularcolumns:: |p{5.6cm}|p{0.9cm}|p{11.0cm}|
207
208.. _cec-tx-status:
209
210.. flat-table:: CEC Transmit Status
211 :header-rows: 0
212 :stub-columns: 0
213 :widths: 3 1 16
214
215 * .. _`CEC-TX-STATUS-OK`:
216
217 - ``CEC_TX_STATUS_OK``
218 - 0x01
219 - The message was transmitted successfully. This is mutually
220 exclusive with :ref:`CEC_TX_STATUS_MAX_RETRIES <CEC-TX-STATUS-MAX-RETRIES>`. Other bits can still
221 be set if earlier attempts met with failure before the transmit
222 was eventually successful.
223 * .. _`CEC-TX-STATUS-ARB-LOST`:
224
225 - ``CEC_TX_STATUS_ARB_LOST``
226 - 0x02
227 - CEC line arbitration was lost.
228 * .. _`CEC-TX-STATUS-NACK`:
229
230 - ``CEC_TX_STATUS_NACK``
231 - 0x04
232 - Message was not acknowledged.
233 * .. _`CEC-TX-STATUS-LOW-DRIVE`:
234
235 - ``CEC_TX_STATUS_LOW_DRIVE``
236 - 0x08
237 - Low drive was detected on the CEC bus. This indicates that a
238 follower detected an error on the bus and requests a
239 retransmission.
240 * .. _`CEC-TX-STATUS-ERROR`:
241
242 - ``CEC_TX_STATUS_ERROR``
243 - 0x10
244 - Some error occurred. This is used for any errors that do not fit
245 the previous two, either because the hardware could not tell which
246 error occurred, or because the hardware tested for other
247 conditions besides those two.
248 * .. _`CEC-TX-STATUS-MAX-RETRIES`:
249
250 - ``CEC_TX_STATUS_MAX_RETRIES``
251 - 0x20
252 - The transmit failed after one or more retries. This status bit is
253 mutually exclusive with :ref:`CEC_TX_STATUS_OK <CEC-TX-STATUS-OK>`. Other bits can still
254 be set to explain which failures were seen.
255
256
257.. tabularcolumns:: |p{5.6cm}|p{0.9cm}|p{11.0cm}|
258
259.. _cec-rx-status:
260
261.. flat-table:: CEC Receive Status
262 :header-rows: 0
263 :stub-columns: 0
264 :widths: 3 1 16
265
266 * .. _`CEC-RX-STATUS-OK`:
267
268 - ``CEC_RX_STATUS_OK``
269 - 0x01
270 - The message was received successfully.
271 * .. _`CEC-RX-STATUS-TIMEOUT`:
272
273 - ``CEC_RX_STATUS_TIMEOUT``
274 - 0x02
275 - The reply to an earlier transmitted message timed out.
276 * .. _`CEC-RX-STATUS-FEATURE-ABORT`:
277
278 - ``CEC_RX_STATUS_FEATURE_ABORT``
279 - 0x04
280 - The message was received successfully but the reply was
281 ``CEC_MSG_FEATURE_ABORT``. This status is only set if this message
282 was the reply to an earlier transmitted message.
283
284
285
286Return Value
287============
288
289On success 0 is returned, on error -1 and the ``errno`` variable is set
290appropriately. The generic error codes are described at the
291:ref:`Generic Error Codes <gen-errors>` chapter.