If there isn't any modifier info coming from the compositor, we go
through our internal image path and pick the best modifier that
supports the image. This causes problems on X11, as it actually
expects the image to be in a linear layout.
Explicitly set the modifier to linear for legacy scanout images,
which specifically indicates that the image doesn't have an
explicit DRM modifier and we should do the safe thing by using
linear.
The naming becomes confusing for scanout with this change,
so the flag is now split into two separate flags, one for controlling
the AFBC optimalness called wsi, the other more directly called
legacy_scanout, which is used for enforcing the linear mod.
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Yiwei Zhang <zzyiwei@chromium.org>
Reviewed-by: Lars-Ivar Hesselberg Simonsen <lars-ivar.simonsen@arm.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/37771>
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