drm: add support for tiled/compressed/etc modifier in addfb2

In DRM/KMS we are lacking a good way to deal with tiled/compressed
formats.  Especially in the case of dmabuf/prime buffer sharing, where
we cannot always rely on under-the-hood flags passed to driver specific
gem-create ioctl to pass around these extra flags.

The proposal is to add a per-plane format modifier.  This allows to, if
necessary, use different tiling patters for sub-sampled planes, etc.
The format modifiers are added at the end of the ioctl struct, so for
legacy userspace it will be zero padded.

v1: original
v1.5: increase modifier to 64b

v2: Incorporate review comments from the big thread, plus a few more.

- Add a getcap so that userspace doesn't have to jump through hoops.
- Allow modifiers only when a flag is set. That way drivers know when
  they're dealing with old userspace and need to fish out e.g. tiling
  from other information.
- After rolling out checks for ->modifier to all drivers I've decided
  that this is way too fragile and needs an explicit opt-in flag. So
  do that instead.
- Add a define (just for documentation really) for the "NONE"
  modifier. Imo we don't need to add mask #defines since drivers
  really should only do exact matches against values defined with
  fourcc_mod_code.
- Drop the Samsung tiling modifier on Rob's request since he's not yet
  sure whether that one is accurate.

v3:
- Also add a new ->modifier[] array to struct drm_framebuffer and fill
  it in drm_helper_mode_fill_fb_struct. Requested by Tvrkto Uruslin.
- Remove TODO in comment and add code comment that modifiers should be
  properly documented, requested by Rob.

Cc: Rob Clark <robdclark@gmail.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Daniel Stone <daniel@fooishbar.org>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Michel Dänzer <michel@daenzer.net>
Signed-off-by: Rob Clark <robdclark@gmail.com> (v1.5)
Reviewed-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>
Acked-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

include/uapi/drm/drm_mode.h

@@ -336,6 +336,7 @@ struct drm_mode_fb_cmd {
 };
 
 #define DRM_MODE_FB_INTERLACED	(1<<0) /* for interlaced framebuffers */
+#define DRM_MODE_FB_MODIFIERS	(1<<1) /* enables ->modifer[] */
 
 struct drm_mode_fb_cmd2 {
 	__u32 fb_id;
@@ -356,10 +357,18 @@ struct drm_mode_fb_cmd2 {
 	 * So it would consist of Y as offsets[0] and UV as
 	 * offsets[1].  Note that offsets[0] will generally
 	 * be 0 (but this is not required).
+	 *
+	 * To accommodate tiled, compressed, etc formats, a per-plane
+	 * modifier can be specified.  The default value of zero
+	 * indicates "native" format as specified by the fourcc.
+	 * Vendor specific modifier token.  This allows, for example,
+	 * different tiling/swizzling pattern on different planes.
+	 * See discussion above of DRM_FORMAT_MOD_xxx.
 	 */
 	__u32 handles[4];
 	__u32 pitches[4]; /* pitch for each plane */
 	__u32 offsets[4]; /* offset of each plane */
+	__u64 modifier[4]; /* ie, tiling, compressed (per plane) */
 };
 
 #define DRM_MODE_FB_DIRTY_ANNOTATE_COPY 0x01