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| author | Hans Verkuil <hans.verkuil@cisco.com> | 2017-02-27 16:53:39 +0300 |
|---|---|---|
| committer | Mauro Carvalho Chehab <mchehab@s-opensource.com> | 2017-03-22 17:13:12 +0300 |
| commit | fabd5bd68f3248761d754ee242a75cd09e6a02f8 (patch) | |
| tree | 32fc3e3e0077167a191f010a66512c243ab72610 /Documentation/media | |
| parent | 491314b8d41bb680f6ddb2632c1a36dd3959d5b3 (diff) | |
| download | linux-fabd5bd68f3248761d754ee242a75cd09e6a02f8.tar.xz | |
[media] cec: document the special unconfigured case
Even when the CEC device is unconfigured due to an invalid physical
address it is still allowed to send a message from 0xf (Unregistered)
to 0 (TV). This is a corner case explicitly allowed by the CEC specification.
Document this corner case.
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Diffstat (limited to 'Documentation/media')
| -rw-r--r-- | Documentation/media/uapi/cec/cec-ioc-receive.rst | 14 |
1 files changed, 14 insertions, 0 deletions
diff --git a/Documentation/media/uapi/cec/cec-ioc-receive.rst b/Documentation/media/uapi/cec/cec-ioc-receive.rst index 3ce7307f55fa..267044f7ac30 100644 --- a/Documentation/media/uapi/cec/cec-ioc-receive.rst +++ b/Documentation/media/uapi/cec/cec-ioc-receive.rst @@ -69,6 +69,18 @@ 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}| @@ -315,6 +327,8 @@ EPERM 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 |