Clarify the description of status bits, particularly w.r.t. ERROR and NACK.
Signed-off-by: Hans Verkuil <hans.verkuil@xxxxxxxxx>
---
diff --git a/Documentation/media/kapi/cec-core.rst b/Documentation/media/kapi/cec-core.rst
index a9f53f069a2d..1d989c544370 100644
--- a/Documentation/media/kapi/cec-core.rst
+++ b/Documentation/media/kapi/cec-core.rst
@@ -246,7 +246,10 @@ CEC_TX_STATUS_LOW_DRIVE:
CEC_TX_STATUS_ERROR:
some unspecified error occurred: this can be one of ARB_LOST
or LOW_DRIVE if the hardware cannot differentiate or something
- else entirely.
+ else entirely. Some hardware only supports OK and FAIL as the
+ result of a transmit, i.e. there is no way to differentiate
+ between the different possible errors. In that case map FAIL
+ to CEC_TX_STATUS_NACK and not to CEC_TX_STATUS_ERROR.
CEC_TX_STATUS_MAX_RETRIES:
could not transmit the message after trying multiple times.
diff --git a/Documentation/media/uapi/cec/cec-ioc-receive.rst b/Documentation/media/uapi/cec/cec-ioc-receive.rst
index bdad4b197bcd..e964074cd15b 100644
--- a/Documentation/media/uapi/cec/cec-ioc-receive.rst
+++ b/Documentation/media/uapi/cec/cec-ioc-receive.rst
@@ -231,26 +231,32 @@ View On' messages from initiator 0xf ('Unregistered') to destination 0 ('TV').
- ``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.
+ 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 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.
+ - 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.
+ retransmission. Optional status, not all hardware can detect this
+ error condition.
* .. _`CEC-TX-STATUS-ERROR`:
- ``CEC_TX_STATUS_ERROR``
@@ -258,14 +264,14 @@ View On' messages from initiator 0xf ('Unregistered') to destination 0 ('TV').
- 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.
+ 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.
+ mutually exclusive with :ref:`CEC_TX_STATUS_OK <CEC-TX-STATUS-OK>`.
+ Other bits can still be set to explain which failures were seen.
.. tabularcolumns:: |p{5.6cm}|p{0.9cm}|p{11.0cm}|
