drm/fourcc: add table describing AMD modifiers bit layout
The table describes how each bit in the u64 value is used. Explicitly
state which values a field can take if we have defines for them. Also
add a note when a field isn't always populated.
Forcing people to update the table when changing the bit layout should
make it more obvious when there's a mistake, I hope.
If we get to the point where the bit layout gets more complicated, it
might be worth it to split the table into multiple tables (e.g. one for
GFX8, one for GFX9+, and so on).
Signed-off-by: Simon Ser <contact@emersion.fr>
Cc: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Cc: Alex Deucher <alexdeucher@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
diff --git a/include/uapi/drm/drm_fourcc.h b/include/uapi/drm/drm_fourcc.h
index ad772e7..bf03bce 100644
--- a/include/uapi/drm/drm_fourcc.h
+++ b/include/uapi/drm/drm_fourcc.h
@@ -1114,6 +1114,25 @@ drm_fourcc_canonicalize_nvidia_format_mod(__u64 modifier)
*
* For multi-plane formats the above surfaces get merged into one plane for
* each format plane, based on the required alignment only.
+ *
+ * Bits Parameter Notes
+ * ----- ------------------------ ---------------------------------------------
+ *
+ * 7:0 TILE_VERSION Values are AMD_FMT_MOD_TILE_VER_*
+ * 12:8 TILE Values are AMD_FMT_MOD_TILE_<version>_*
+ * 13 DCC
+ * 14 DCC_RETILE
+ * 15 DCC_PIPE_ALIGN
+ * 16 DCC_INDEPENDENT_64B
+ * 17 DCC_INDEPENDENT_128B
+ * 19:18 DCC_MAX_COMPRESSED_BLOCK Values are AMD_FMT_MOD_DCC_BLOCK_*
+ * 20 DCC_CONSTANT_ENCODE
+ * 23:21 PIPE_XOR_BITS Only for some chips
+ * 26:24 BANK_XOR_BITS Only for some chips
+ * 29:27 PACKERS Only for some chips
+ * 32:30 RB Only for some chips
+ * 35:33 PIPE Only for some chips
+ * 55:36 - Reserved for future use, must be zero
*/
#define AMD_FMT_MOD fourcc_mod_code(AMD, 0)
