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UPSTREAM: drm_dp_cec: add note about good MegaChips 2900 CEC support

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A big problem with DP CEC-Tunneling-over-AUX is that it is tricky
to find adapters with a chipset that supports this AND where the
manufacturer actually connected the HDMI CEC line to the chipset.

Add a mention of the MegaChips 2900 chipset which seems to support
this feature well.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180827075820.41109-3-hverkuil@xs4all.nl
(cherry picked from commit 9bcf6d9868)

Change-Id: Idd9a225357a5b3bbb14287cc1f5b13630d0bd449
Signed-off-by: Algea Cao <algea.cao@rock-chips.com>
This commit is contained in:
Hans Verkuil
2018-08-27 09:58:17 +02:00
committed by Tao Huang
parent 51b3852a7f
commit 349e07ffdf
1 changed files with 3 additions and 1 deletions
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4
drivers/gpu/drm/drm_dp_cec.c
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@@ -16,7 +16,9 @@
* here. Quite a few active (mini-)DP-to-HDMI or USB-C-to-HDMI adapters
* have a converter chip that supports CEC-Tunneling-over-AUX (usually the
* Parade PS176), but they do not wire up the CEC pin, thus making CEC
* useless.
* useless. Note that MegaChips 2900-based adapters appear to have good
* support for CEC tunneling. Those adapters that I have tested using
* this chipset all have the CEC line connected.
*
* Sadly there is no way for this driver to know this. What happens is
* that a /dev/cecX device is created that is isolated and unable to see