[PATCH] drm/edid: Don't send non-zero YQ in AVI infoframe for HDMI 1.x sinks

[Eric Anholt]

Ville Syrjälä <ville.syrjala at linux.intel.com> writes:

> On Wed, Nov 08, 2017 at 12:17:28PM -0800, Eric Anholt wrote:
>> Ville Syrjala <ville.syrjala at linux.intel.com> writes:
>> 
>> > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
>> >
>> > Apparently some sinks look at the YQ bits even when receiving RGB,
>> > and they get somehow confused when they see a non-zero YQ value.
>> > So we can't just blindly follow CEA-861-F and set YQ to match the
>> > RGB range.
>> >
>> > Unfortunately there is no good way to tell whether the sink
>> > designer claims to have read CEA-861-F. The CEA extension block
>> > revision number has generally been stuck at 3 since forever,
>> > and even a very recently manufactured sink might be based on
>> > an old design so the manufacturing date doesn't seem like
>> > something we can use. In lieu of better information let's
>> > follow CEA-861-F only for HDMI 2.0 sinks, since HDMI 2.0 is
>> > based on CEA-861-F. For HDMI 1.x sinks we'll always set YQ=0.
>> >
>> > The alternative would of course be to always set YQ=0. And if
>> > we ever encounter a HDMI 2.0+ sink with this bug that's what
>> > we'll probably have to do.
>> 
>> Should vc4 be doing anything special for HDMI2 sinks, if it's an HDMI1.4
>> source?
>
> As long as you stick to < 340 MHz modes you shouldn't have to do
> anything. For >=340 MHz you'd need to use some new HDMI 2.0 features.
>
> Looks like vc4 crtc .mode_valid() doesn't do much. I presume it's up
> to bridges/encoders to filter out most things that aren't supported?

I had a patch for that at
https://patchwork.freedesktop.org/series/30680/ -- fedora folks had run
into trouble with 4k monitors.
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