diff options
Diffstat (limited to 'Documentation/media/uapi/cec/cec-ioc-receive.rst')
| -rw-r--r-- | Documentation/media/uapi/cec/cec-ioc-receive.rst | 360 |
1 files changed, 360 insertions, 0 deletions
diff --git a/Documentation/media/uapi/cec/cec-ioc-receive.rst b/Documentation/media/uapi/cec/cec-ioc-receive.rst new file mode 100644 index 000000000..ae5a39ade --- /dev/null +++ b/Documentation/media/uapi/cec/cec-ioc-receive.rst @@ -0,0 +1,360 @@ +.. -*- coding: utf-8; mode: rst -*- + +.. _CEC_TRANSMIT: +.. _CEC_RECEIVE: + +*********************************** +ioctls CEC_RECEIVE and CEC_TRANSMIT +*********************************** + +Name +==== + +CEC_RECEIVE, CEC_TRANSMIT - Receive or transmit a CEC message + + +Synopsis +======== + +.. cpp:function:: int ioctl( int fd, int request, struct cec_msg *argp ) + +Arguments +========= + +``fd`` + File descriptor returned by :ref:`open() <cec-func-open>`. + +``request`` + CEC_RECEIVE, CEC_TRANSMIT + +``argp`` + + +Description +=========== + +.. note:: This documents the proposed CEC API. This API is not yet finalized + and is currently only available as a staging kernel module. + +To receive a CEC message the application has to fill in the +``timeout`` field of :c:type:`struct 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 +:c:type:`struct 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. + + +.. _cec-msg: + +.. flat-table:: struct cec_msg + :header-rows: 0 + :stub-columns: 0 + :widths: 1 1 16 + + + - .. row 1 + + - __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(2)`. + + - .. row 2 + + - __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(2)`. + + - .. row 3 + + - __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. + + - .. row 4 + + - __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. + + - .. row 5 + + - __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. + + - .. row 6 + + - __u32 + + - ``flags`` + + - Flags. No flags are defined yet, so set this to 0. + + - .. row 7 + + - __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 messages was received, not transmitted. + + - .. row 8 + + - __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. + + - .. row 8 + + - __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>`. + + - .. row 9 + + - __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. + + - .. row 10 + + - __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 messages was received, not transmitted. + + - .. row 11 + + - __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. + + - .. row 12 + + - __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. + + - .. row 13 + + - __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. + + - .. row 14 + + - __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. + + + +.. _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. + + - .. _`CEC-TX-STATUS-NACK`: + + - ``CEC_TX_STATUS_NACK`` + + - 0x04 + + - Message was not acknowledged. + + - .. _`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. + + - .. _`CEC-TX-STATUS-ERROR`: + + - ``CEC_TX_STATUS_ERROR`` + + - 0x10 + + - Some error occurred. This is used for any errors that do not fit + the previous two, either because the hardware could not tell which + error occurred, or because the hardware tested for other + conditions besides those two. + + - .. _`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-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. + + + +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. |