[PATCH] drm/amdgpu: Ensure that the modifier requested is supported by plane.

[Mark Yacoub]

On Wed, Mar 24, 2021 at 8:10 AM Daniel Stone <daniel at fooishbar.org> wrote:
>
> On Wed, 24 Mar 2021 at 10:53, Bas Nieuwenhuizen <bas at basnieuwenhuizen.nl> wrote:
>>
>> On Wed, Mar 24, 2021 at 11:13 AM Michel Dänzer <michel at daenzer.net> wrote:
>>>
>>> No modifier support does not imply linear. It's generally signalled via DRM_FORMAT_MOD_INVALID, which roughly means "tiling is determined by driver specific mechanisms".
So you mean it would make more sense to be more explicit in handling
DRM_FORMAT_MOD_INVALID as an incoming modifier (which will, just like
DRM_FORMAT_MOD_LINEAR, will return true in
dm_plane_format_mod_supported)?
>>
>>
>> Doesn't quite work that way in the kernel sadly. If you don't set DRM_MODE_FB_MODIFIERS then the modifier fields have to be 0 (which happens to alias DRM_FORMAT_MOD_LINEAR and then now deprecated DRM_FORMAT_MOD_NONE). This is verified in shared drm code.
>>
>> (and all userspace code I've seen simply doesn't set DRM_MODE_FB_MODIFIERS if the incoming modifier is DRM_FORMAT_MOD_INVALID)
>
>
> Yes, but even though the field is zero, the lack of the flag means it must be treated as INVALID. If the kernel is not doing this, the kernel is objectively wrong. (And I know it doesn't do this in most cases, because otherwise I wouldn't be able to use this GNOME session on an Intel laptop, where modifiers are blacklisted.)
>
> Cheers,
> Daniel