The check for "no modifier specified" in drmmode_is_format_supported()
should check for DRM_FORMAT_MOD_INVALID, not for zero, as zero actually
means DRM_FORMAT_MOD_LINEAR.
This allows page-flipping again when appropriate, as
tested under nouveau and ati drivers.
Fixes: 9d147305b4 ("modesetting: Check if buffer format is supported when flipping")
Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>
757e0ee188