[PATCH] amd/display: remove ChromeOS workaround

[Paul Menzel]

Dear Simon,


Am 19.10.21 um 10:10 schrieb Simon Ser:
> On Tuesday, October 19th, 2021 at 01:21, Paul Menzel <pmenzel at molgen.mpg.de> wrote:
> 
>> Am 19.10.21 um 01:06 schrieb Simon Ser:
>>> On Tuesday, October 19th, 2021 at 01:03, Paul Menzel wrote:
>>>
>>>> Excuse my ignorance. Reading the commit message, there was a Linux
>>>> kernel change, that broke Chrome OS userspace, right? If so, and we do
>>>> not know if there is other userspace using the API incorrectly,
>>>> shouldn’t the patch breaking Chrome OS userspace be reverted to adhere
>>>> to Linux’ no-regression rule?
>>>
>>> No. There was a ChromeOS bug which has been thought to be an amdgpu bug. But
>>> fixing that "bug" breaks other user-space.
>>
>> Thank you for the explanation. I guess the bug was only surfacing
>> because Chrome OS device, like Chromebooks, are only using AMD hardware
>> since a short while (maybe last year).
>>
>> Reading your message *amdgpu: atomic API and cursor/overlay planes* [1]
>> again, it says:
>>
>>> Up until now we were using cursor and overlay planes in gamescope [3],
>>> but some changes in the amdgpu driver [1] makes us unable to use planes
>>
>> So this statement was incorrect? Which changes are that? Or did Chrome
>> OS ever work correctly with an older Linux kernel or not?
> 
> The sequence of events is as follows:
> 
> - gamescope can use cursor and overlay planes.
> - ChromeOS-specific commit lands, fixing some ChromeOS issues related to video
>    playback. This breaks gamescope overlays.

I guess, I am confused, which Chrome OS specific commit that is. Is it 
one of the reverted commits below? Which one?

1.  ddab8bd788f5 ("drm/amd/display: Fix two cursor duplication
when using overlay")
2.  e7d9560aeae5 ("Revert "drm/amd/display: Fix overlay validation by 
considering cursors"")

> - Discussion to restrict the ChromeOS-specific logic to ChromeOS, or to revert
>    it, either of these fix gamescope.
> 
> Given this, I don't see how the quoted statement is incorrect? Maybe I'm
> missing something?

Your reply from August 2021 to commit ddab8bd788f5 (drm/amd/display: Fix 
two cursor duplication when using overlay) from April 2021 [2]:

> Hm. This patch causes a regression for me. I was using primary + overlay
> not covering the whole primary plane + cursor before. This patch breaks it.
> 
> This patch makes the overlay plane very useless for me, because the primary
> plane is always under the overlay plane.

So, I would have thought, everything worked fine before some Linux 
kernel commit changed behavior, and regressed userspace.


Kind regards,

Paul


[2]: 
https://lore.kernel.org/amd-gfx/SrcUnUUGJquVgjp9P79uV8sv6s-kMHG4wp0S3b4Nh9ksi29EIOye5edofuXkDLRvGfvkkRpQZ9JM7MNqew2B3kFUhaxsonDRXprkAYXaQUo=@emersion.fr/