From fabd5bd68f3248761d754ee242a75cd09e6a02f8 Mon Sep 17 00:00:00 2001 From: Hans Verkuil Date: Mon, 27 Feb 2017 10:53:39 -0300 Subject: [PATCH] [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 Signed-off-by: Mauro Carvalho Chehab --- Documentation/media/uapi/cec/cec-ioc-receive.rst | 14 ++++++++++++++ 1 file changed, 14 insertions(+) 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 ` 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 ` 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 -- 2.20.1