Mario Kleiner authored Apr 24, 2018 and Adam Jackson committed Apr 25, 2018

Both xf86-video-intel and xf86-video-nouveau cause OpenGL clients to
fail when used with DRI3 on server 1.20 with Mesa 18.1.

Reason is that the servers DRI3 version is now unconditionally reported
as DRI3 1.2 to 1.2 capable clients. This causes clients using Mesa 18.1
to use the new DRI 3.2 requests DRI3GetSupportedModifiers,
DRI3PixmapFromBuffers, etc. Drivers other than modesetting-ddx do not
support the needed hooks like info->pixmap_from_fds or
info->get_formats, info->get_modifiers. Unfortunately we can't simply
report the servers DRI3 version as 1.0 in this case, as the reported
version can not be specific to a X-Screen, and different screens may
have drivers with different capabilities.

Luckily the server has fallbacks to ->pixmap_from_fd, ->fd_from_pixmap,
and simply reporting an empty set of supported modifiers for the
DRI3GetSupportedModifiers request if the ddx doesn't support DRI 3.2.

Clients like Mesa 18.1's dri3 loader respond to the empty set of
reported modifiers by falling back to a dri driver selected buffer
format (image->createImageWithModifiers responds to a NULL modifier_list
by acting like ->createImage()). This works, but Mesa 18.1 will still
try to use the DRI3PixmapFromBuffers request to create the corresponding
pixmap, just passing in a modifier that corresponds to whatever tiling
the dri driver selected by default. To prevent this request - and
thereby the client - from failing with a BadImplementation error, remove
the check for modifier == DRM_MOD_FORMAT_INVALID in the pixmap_from_fd
fallback path of dri3_pixmap_from_fds() and trust that if we hit the
fallback path then the client will have passed a buffer with some driver
specific default tiling that can be handled by pixmap_from_fd.

Another approach would be for Mesa's dri3 loader to keep track how a
buffer was created (with explicit modifiers or not), and then call
DRI3PixmapFromBuffers or DRI3PixmapFromBuffer, but then any future DRI3
client implementation would need to be fixed, so the server side is
probably the better place for this.

Tested on Intel Ivybridge and NVidia Pascal.

Fixes: 6e7c40f6

 ("dri3: Add multi-planar/modifier buffer requests")
Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Cc: Daniel Stone <daniels@collabora.com>
Cc: Louis-Francis Ratté-Boulianne <lfrb@collabora.com>
Tested-by: Mike Lothian <mike@fireburn.co.uk>
Reviewed-by: Adam Jackson <ajax@redhat.com>