On Wed, Mar 24, 2021 at 8:10 AM Daniel Stone <dan...@fooishbar.org> wrote:
>
> On Wed, 24 Mar 2021 at 10:53, Bas Nieuwenhuizen <b...@basnieuwenhuizen.nl>
> wrote:
>>
>> On Wed, Mar 24, 2021 at 11:13 AM Michel Dänzer <mic...@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
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