diff options
Diffstat (limited to '')
| -rw-r--r-- | Documentation/userspace-api/media/cec/cec-ioc-receive.rst | 382 |
1 files changed, 382 insertions, 0 deletions
diff --git a/Documentation/userspace-api/media/cec/cec-ioc-receive.rst b/Documentation/userspace-api/media/cec/cec-ioc-receive.rst new file mode 100644 index 000000000..b2fc051e9 --- /dev/null +++ b/Documentation/userspace-api/media/cec/cec-ioc-receive.rst @@ -0,0 +1,382 @@ +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later +.. c:namespace:: CEC + +.. _CEC_TRANSMIT: +.. _CEC_RECEIVE: + +*********************************** +ioctls CEC_RECEIVE and CEC_TRANSMIT +*********************************** + +Name +==== + +CEC_RECEIVE, CEC_TRANSMIT - Receive or transmit a CEC message + +Synopsis +======== + +.. c:macro:: CEC_RECEIVE + +``int ioctl(int fd, CEC_RECEIVE, struct cec_msg *argp)`` + +.. c:macro:: CEC_TRANSMIT + +``int ioctl(int fd, CEC_TRANSMIT, struct cec_msg *argp)`` + +Arguments +========= + +``fd`` + File descriptor returned by :c:func:`open()`. + +``argp`` + Pointer to struct cec_msg. + +Description +=========== + +To receive a CEC message the application has to fill in the +``timeout`` field of struct :c:type:`cec_msg` and pass it to +:ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`. +If the file descriptor is in non-blocking mode and there are no received +messages pending, then it will return -1 and set errno to the ``EAGAIN`` +error code. If the file descriptor is in blocking mode and ``timeout`` +is non-zero and no message arrived within ``timeout`` milliseconds, then +it will return -1 and set errno to the ``ETIMEDOUT`` error code. + +A received message can be: + +1. a message received from another CEC device (the ``sequence`` field will + be 0). +2. the result of an earlier non-blocking transmit (the ``sequence`` field will + be non-zero). + +To send a CEC message the application has to fill in the struct +:c:type:`cec_msg` and pass it to :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`. +The :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` is only available if +``CEC_CAP_TRANSMIT`` is set. If there is no more room in the transmit +queue, then it will return -1 and set errno to the ``EBUSY`` error code. +The transmit queue has enough room for 18 messages (about 1 second worth +of 2-byte messages). Note that the CEC kernel framework will also reply +to core messages (see :ref:`cec-core-processing`), so it is not a good +idea to fully fill up the transmit queue. + +If the file descriptor is in non-blocking mode then the transmit will +return 0 and the result of the transmit will be available via +:ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>` once the transmit has finished +(including waiting for a reply, if requested). + +The ``sequence`` field is filled in for every transmit and this can be +checked against the received messages to find the corresponding transmit +result. + +Normally calling :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` when the physical +address is invalid (due to e.g. a disconnect) will return ``ENONET``. + +However, the CEC specification allows sending messages from 'Unregistered' to +'TV' when the physical address is invalid since some TVs pull the hotplug detect +pin of the HDMI connector low when they go into standby, or when switching to +another input. + +When the hotplug detect pin goes low the EDID disappears, and thus the +physical address, but the cable is still connected and CEC still works. +In order to detect/wake up the device it is allowed to send poll and 'Image/Text +View On' messages from initiator 0xf ('Unregistered') to destination 0 ('TV'). + +.. tabularcolumns:: |p{1.0cm}|p{3.5cm}|p{13.0cm}| + +.. c:type:: cec_msg + +.. cssclass:: longtable + +.. flat-table:: struct cec_msg + :header-rows: 0 + :stub-columns: 0 + :widths: 1 1 16 + + * - __u64 + - ``tx_ts`` + - Timestamp in ns of when the last byte of the message was transmitted. + The timestamp has been taken from the ``CLOCK_MONOTONIC`` clock. To access + the same clock from userspace use :c:func:`clock_gettime`. + * - __u64 + - ``rx_ts`` + - Timestamp in ns of when the last byte of the message was received. + The timestamp has been taken from the ``CLOCK_MONOTONIC`` clock. To access + the same clock from userspace use :c:func:`clock_gettime`. + * - __u32 + - ``len`` + - The length of the message. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` this is filled in + by the application. The driver will fill this in for + :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` it will be + filled in by the driver with the length of the reply message if ``reply`` was set. + * - __u32 + - ``timeout`` + - The timeout in milliseconds. This is the time the device will wait + for a message to be received before timing out. If it is set to 0, + then it will wait indefinitely when it is called by :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`. + If it is 0 and it is called by :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`, + then it will be replaced by 1000 if the ``reply`` is non-zero or + ignored if ``reply`` is 0. + * - __u32 + - ``sequence`` + - A non-zero sequence number is automatically assigned by the CEC framework + for all transmitted messages. It is used by the CEC framework when it queues + the transmit result (when transmit was called in non-blocking mode). This + allows the application to associate the received message with the original + transmit. + * - __u32 + - ``flags`` + - Flags. See :ref:`cec-msg-flags` for a list of available flags. + * - __u8 + - ``tx_status`` + - The status bits of the transmitted message. See + :ref:`cec-tx-status` for the possible status values. It is 0 if + this message was received, not transmitted. + * - __u8 + - ``msg[16]`` + - The message payload. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` this is filled in by the + application. The driver will fill this in for :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`. + For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` it will be filled in by the driver with + the payload of the reply message if ``timeout`` was set. + * - __u8 + - ``reply`` + - Wait until this message is replied. If ``reply`` is 0 and the + ``timeout`` is 0, then don't wait for a reply but return after + transmitting the message. Ignored by :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`. + The case where ``reply`` is 0 (this is the opcode for the Feature Abort + message) and ``timeout`` is non-zero is specifically allowed to make it + possible to send a message and wait up to ``timeout`` milliseconds for a + Feature Abort reply. In this case ``rx_status`` will either be set + to :ref:`CEC_RX_STATUS_TIMEOUT <CEC-RX-STATUS-TIMEOUT>` or + :ref:`CEC_RX_STATUS_FEATURE_ABORT <CEC-RX-STATUS-FEATURE-ABORT>`. + + If the transmitter message is ``CEC_MSG_INITIATE_ARC`` then the ``reply`` + values ``CEC_MSG_REPORT_ARC_INITIATED`` and ``CEC_MSG_REPORT_ARC_TERMINATED`` + are processed differently: either value will match both possible replies. + The reason is that the ``CEC_MSG_INITIATE_ARC`` message is the only CEC + message that has two possible replies other than Feature Abort. The + ``reply`` field will be updated with the actual reply so that it is + synchronized with the contents of the received message. + * - __u8 + - ``rx_status`` + - The status bits of the received message. See + :ref:`cec-rx-status` for the possible status values. It is 0 if + this message was transmitted, not received, unless this is the + reply to a transmitted message. In that case both ``rx_status`` + and ``tx_status`` are set. + * - __u8 + - ``tx_status`` + - The status bits of the transmitted message. See + :ref:`cec-tx-status` for the possible status values. It is 0 if + this message was received, not transmitted. + * - __u8 + - ``tx_arb_lost_cnt`` + - A counter of the number of transmit attempts that resulted in the + Arbitration Lost error. This is only set if the hardware supports + this, otherwise it is always 0. This counter is only valid if the + :ref:`CEC_TX_STATUS_ARB_LOST <CEC-TX-STATUS-ARB-LOST>` status bit is set. + * - __u8 + - ``tx_nack_cnt`` + - A counter of the number of transmit attempts that resulted in the + Not Acknowledged error. This is only set if the hardware supports + this, otherwise it is always 0. This counter is only valid if the + :ref:`CEC_TX_STATUS_NACK <CEC-TX-STATUS-NACK>` status bit is set. + * - __u8 + - ``tx_low_drive_cnt`` + - A counter of the number of transmit attempts that resulted in the + Arbitration Lost error. This is only set if the hardware supports + this, otherwise it is always 0. This counter is only valid if the + :ref:`CEC_TX_STATUS_LOW_DRIVE <CEC-TX-STATUS-LOW-DRIVE>` status bit is set. + * - __u8 + - ``tx_error_cnt`` + - A counter of the number of transmit errors other than Arbitration + Lost or Not Acknowledged. This is only set if the hardware + supports this, otherwise it is always 0. This counter is only + valid if the :ref:`CEC_TX_STATUS_ERROR <CEC-TX-STATUS-ERROR>` status bit is set. + +.. tabularcolumns:: |p{6.2cm}|p{1.0cm}|p{10.3cm}| + +.. _cec-msg-flags: + +.. flat-table:: Flags for struct cec_msg + :header-rows: 0 + :stub-columns: 0 + :widths: 3 1 4 + + * .. _`CEC-MSG-FL-REPLY-TO-FOLLOWERS`: + + - ``CEC_MSG_FL_REPLY_TO_FOLLOWERS`` + - 1 + - If a CEC transmit expects a reply, then by default that reply is only sent to + the filehandle that called :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`. If this + flag is set, then the reply is also sent to all followers, if any. If the + filehandle that called :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` is also a + follower, then that filehandle will receive the reply twice: once as the + result of the :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`, and once via + :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`. + + * .. _`CEC-MSG-FL-RAW`: + + - ``CEC_MSG_FL_RAW`` + - 2 + - Normally CEC messages are validated before transmitting them. If this + flag is set when :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` is called, + then no validation takes place and the message is transmitted as-is. + This is useful when debugging CEC issues. + This flag is only allowed if the process has the ``CAP_SYS_RAWIO`` + capability. If that is not set, then the ``EPERM`` error code is + returned. + +.. tabularcolumns:: |p{5.6cm}|p{0.9cm}|p{11.0cm}| + +.. _cec-tx-status: + +.. flat-table:: CEC Transmit Status + :header-rows: 0 + :stub-columns: 0 + :widths: 3 1 16 + + * .. _`CEC-TX-STATUS-OK`: + + - ``CEC_TX_STATUS_OK`` + - 0x01 + - The message was transmitted successfully. This is mutually + exclusive with :ref:`CEC_TX_STATUS_MAX_RETRIES <CEC-TX-STATUS-MAX-RETRIES>`. + Other bits can still be set if earlier attempts met with failure before + the transmit was eventually successful. + * .. _`CEC-TX-STATUS-ARB-LOST`: + + - ``CEC_TX_STATUS_ARB_LOST`` + - 0x02 + - CEC line arbitration was lost, i.e. another transmit started at the + same time with a higher priority. Optional status, not all hardware + can detect this error condition. + * .. _`CEC-TX-STATUS-NACK`: + + - ``CEC_TX_STATUS_NACK`` + - 0x04 + - Message was not acknowledged. Note that some hardware cannot tell apart + a 'Not Acknowledged' status from other error conditions, i.e. the result + of a transmit is just OK or FAIL. In that case this status will be + returned when the transmit failed. + * .. _`CEC-TX-STATUS-LOW-DRIVE`: + + - ``CEC_TX_STATUS_LOW_DRIVE`` + - 0x08 + - Low drive was detected on the CEC bus. This indicates that a + follower detected an error on the bus and requests a + retransmission. Optional status, not all hardware can detect this + error condition. + * .. _`CEC-TX-STATUS-ERROR`: + + - ``CEC_TX_STATUS_ERROR`` + - 0x10 + - Some error occurred. This is used for any errors that do not fit + ``CEC_TX_STATUS_ARB_LOST`` or ``CEC_TX_STATUS_LOW_DRIVE``, either because + the hardware could not tell which error occurred, or because the hardware + tested for other conditions besides those two. Optional status. + * .. _`CEC-TX-STATUS-MAX-RETRIES`: + + - ``CEC_TX_STATUS_MAX_RETRIES`` + - 0x20 + - The transmit failed after one or more retries. This status bit is + mutually exclusive with :ref:`CEC_TX_STATUS_OK <CEC-TX-STATUS-OK>`. + Other bits can still be set to explain which failures were seen. + * .. _`CEC-TX-STATUS-ABORTED`: + + - ``CEC_TX_STATUS_ABORTED`` + - 0x40 + - The transmit was aborted due to an HDMI disconnect, or the adapter + was unconfigured, or a transmit was interrupted, or the driver + returned an error when attempting to start a transmit. + * .. _`CEC-TX-STATUS-TIMEOUT`: + + - ``CEC_TX_STATUS_TIMEOUT`` + - 0x80 + - The transmit timed out. This should not normally happen and this + indicates a driver problem. + +.. tabularcolumns:: |p{5.6cm}|p{0.9cm}|p{11.0cm}| + +.. _cec-rx-status: + +.. flat-table:: CEC Receive Status + :header-rows: 0 + :stub-columns: 0 + :widths: 3 1 16 + + * .. _`CEC-RX-STATUS-OK`: + + - ``CEC_RX_STATUS_OK`` + - 0x01 + - The message was received successfully. + * .. _`CEC-RX-STATUS-TIMEOUT`: + + - ``CEC_RX_STATUS_TIMEOUT`` + - 0x02 + - The reply to an earlier transmitted message timed out. + * .. _`CEC-RX-STATUS-FEATURE-ABORT`: + + - ``CEC_RX_STATUS_FEATURE_ABORT`` + - 0x04 + - The message was received successfully but the reply was + ``CEC_MSG_FEATURE_ABORT``. This status is only set if this message + was the reply to an earlier transmitted message. + * .. _`CEC-RX-STATUS-ABORTED`: + + - ``CEC_RX_STATUS_ABORTED`` + - 0x08 + - The wait for a reply to an earlier transmitted message was aborted + because the HDMI cable was disconnected, the adapter was unconfigured + or the :ref:`CEC_TRANSMIT <CEC_RECEIVE>` that waited for a + reply was interrupted. + + +Return Value +============ + +On success 0 is returned, on error -1 and the ``errno`` variable is set +appropriately. The generic error codes are described at the +:ref:`Generic Error Codes <gen-errors>` chapter. + +The :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>` can return the following +error codes: + +EAGAIN + No messages are in the receive queue, and the filehandle is in non-blocking mode. + +ETIMEDOUT + The ``timeout`` was reached while waiting for a message. + +ERESTARTSYS + The wait for a message was interrupted (e.g. by Ctrl-C). + +The :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` can return the following +error codes: + +ENOTTY + The ``CEC_CAP_TRANSMIT`` capability wasn't set, so this ioctl is not supported. + +EPERM + The CEC adapter is not configured, i.e. :ref:`ioctl CEC_ADAP_S_LOG_ADDRS <CEC_ADAP_S_LOG_ADDRS>` + has never been called, or ``CEC_MSG_FL_RAW`` was used from a process that + did not have the ``CAP_SYS_RAWIO`` capability. + +ENONET + The CEC adapter is not configured, i.e. :ref:`ioctl CEC_ADAP_S_LOG_ADDRS <CEC_ADAP_S_LOG_ADDRS>` + was called, but the physical address is invalid so no logical address was claimed. + An exception is made in this case for transmits from initiator 0xf ('Unregistered') + to destination 0 ('TV'). In that case the transmit will proceed as usual. + +EBUSY + Another filehandle is in exclusive follower or initiator mode, or the filehandle + is in mode ``CEC_MODE_NO_INITIATOR``. This is also returned if the transmit + queue is full. + +EINVAL + The contents of struct :c:type:`cec_msg` is invalid. + +ERESTARTSYS + The wait for a successful transmit was interrupted (e.g. by Ctrl-C). |