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

[Rob Clark]

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.

TODO how best to deal with assignment of modifier token values?  The
rough idea was to namespace things with an 8bit vendor-id, and then
beyond that it is treated as an opaque value.  But that was a relatively
arbitrary choice.  There are cases where same tiling pattern and/or
compression is supported by various different vendors.  So we should
standardize to use the vendor-id and value of the first one who
documents the format?

TODO move definition of tokens to drm_fourcc.h?

Signed-off-by: Rob Clark <robdclark at gmail.com>
---
 include/uapi/drm/drm_mode.h | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
index aae71cb..c43648c 100644
--- a/include/uapi/drm/drm_mode.h
+++ b/include/uapi/drm/drm_mode.h
@@ -330,6 +330,28 @@ struct drm_mode_fb_cmd {
 
 #define DRM_MODE_FB_INTERLACED	(1<<0) /* for interlaced framebuffers */
 
+/*
+ * Format Modifiers:
+ *
+ * Format modifiers describe, typically, a re-ordering or modification
+ * of the data in a plane of an FB.  This can be used to express tiled/
+ * swizzled formats, or compression, or a combination of the two.
+ *
+ * The upper 8 bits of the format modifier are a vendor-id as assigned
+ * below.  The lower 24 bits are assigned as vendor sees fit.
+ */
+
+/* Vendor Ids: */
+#define DRM_FOURCC_MOD_VENDOR_SAMSUNG 0x03
+/* ... more */
+
+#define DRM_FOURCC_MOD(vendor, name) (((DRM_FOURCC_MOD_VENDOR_## vendor) << 24) | val)
+
+/* Modifier values: */
+/* 64x32 macroblock, ie NV12MT: */
+#define DRM_FOURCC_MOD_SAMSUNG_64_32_TILE DRM_FOURCC_MOD(SAMSUNG, 123)
+/* ... more */
+
 struct drm_mode_fb_cmd2 {
 	__u32 fb_id;
 	__u32 width, height;
@@ -349,10 +371,18 @@ 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_FOURCC_MOD_xxx.
 	 */
 	__u32 handles[4];
 	__u32 pitches[4]; /* pitch for each plane */
 	__u32 offsets[4]; /* offset of each plane */
+	__u32 modifier[4]; /* ie, tiling, compressed (per plane) */
 };
 
 #define DRM_MODE_FB_DIRTY_ANNOTATE_COPY 0x01
-- 
2.1.0