On Wed, 24 Mar 2021 at 10:53, Bas Nieuwenhuizen <bas@xxxxxxxxxxxxxxxxxxx> 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".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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