HDMI Aspect Ratio

[Alex Deucher]

On Thu, Oct 19, 2017 at 12:32 PM, Rob Clark <robdclark at gmail.com> wrote:
> On Wed, Oct 18, 2017 at 4:06 PM, Lloyd Atkinson <latkinso at codeaurora.org> wrote:
>> Hi folks,
>>
>> We're looking at 4K HDMI mode support, and noticed aspect ratio support
>> is in flux.
>>
>> Aspect ratio parsing was added to the mode:
>> https://patchwork.kernel.org/patch/9271401/
>>
>> But later reverted:
>> https://patchwork.kernel.org/patch/9410765/
>>
>> We're finding that since aspect ratio information isn't supported, modes
>> conflict, and the userspace isn't able to see the full list of modes.
>>
>> Similarly, there's a case where two modes differ only by aspect_ratio
>> and vrefresh. In drm_edid.c, within drm_display_mode_from_vic_index,
>> newmode->vrefresh is forcibly being cleared to 0. Since refresh rate is
>> forced to 0, and aspect ratio isn’t considered in general, the modes
>> collide and we can’t advertise one of the modes.
>>
>> https://github.com/torvalds/linux/blob/v4.14-rc4/drivers/gpu/drm/drm_edid.c#L3153
>>
>> Have there been any follow-up discussions on this topic?
>>
>> What is the reason to clear the vrefresh within
>> drm_display_mode_from_vic_index?
>
> +Ville who might remember the history..
>
> I don't remember if we found a userspace app that was broken, or if
> reverting was an "abundance of caution" thing (which is equally valid,
> it is basically impossible to track down and test "all of
> userspace"..)
>

Wasn't there an issue with SNA?

Alex

> Adding a cap to let userspace opt-in to the new behaviour seems like a
> sensible approach, and one that we've used before.>
> BR,
> -R
>
>> Thanks,
>> Lloyd Atkinson
>>
>> --
>> QUALCOMM Canada, on behalf of Qualcomm Innovation Center, Inc. is a member
>> of Code Aurora Forum, hosted by The Linux Foundation
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