[Intel-gfx] [PATCH] drm/i915: Use AUX for backlight only if eDP 1.4 or later

[Puthikorn Voravootivat]

> But now you're suggesting another arbitrary narrow selection of panels
> based on limited evidence.

I understand your point that the panel I observe is not the
representative of the real world.

My point is that we don't know that the panel will work or not unless
we test all panel in the world.
And blacklist would be too much work to maintain and whitelist would
make this code too limited.
As standard adoption should be better over time, I suggest that the
newer panel should have
better implement of the standard than older panel. And I suggest that
eDP 1.4 should be a good
heuristic for the "newer panel" based on these 2 reasons

1. Even though it is a limited evident, David and I independently saw
unrelated eDP 1.3 panel that
implement this feature incorrectly.
2. eDP 1.4 is the first version that support AUX backlight enablement.
TCON vendor probably also
make sure the AUX backlight brightness ajustment works when testing
that feature.

Is this make sense?

Thanks.

On Mon, Jul 31, 2017 at 3:55 AM, Jani Nikula
<jani.nikula at linux.intel.com> wrote:
> On Mon, 24 Jul 2017, Puthikorn Voravootivat <puthik at chromium.org> wrote:
>> I saw a DP 1.3 panel that advertise AUX backlight brightness control
>> but not working properly. So it should work but not in real world.
>> I think that is good reason enough to add this as a heuristic.
>
> Are you suggesting the one panel you mention is representative of the
> real world?
>
> Granted, the original aux backlight implementation supported a very
> narrow selection of panels. I believe this is the very reason you are
> working on this patch series.
>
> But now you're suggesting another arbitrary narrow selection of panels
> based on limited evidence.
>
>
> BR,
> Jani.
>
>
> --
> Jani Nikula, Intel Open Source Technology Center