drm: Create a format/modifier blob

Updated blob layout (Rob, Daniel, Kristian, xerpi)

v2:
* Removed __packed, and alignment (.+)
* Fix indent in drm_format_modifier fields (Liviu)
* Remove duplicated modifier > 64 check (Liviu)
* Change comment about modifier (Liviu)
* Remove arguments to blob creation, use plane instead (Liviu)
* Fix data types (Ben)
* Make the blob part of uapi (Daniel)

v3:
Remove unused ret field.
Change i, and j to unsigned int (Emil)

v4:
Use plane->modifier_count instead of recounting (Daniel)

v5:
Rename modifiers to modifiers_property (Ville)
Use sizeof(__u32) instead to reflect UAPI nature (Ville)
Make BUILD_BUG_ON for blob header size

Cc: Rob Clark <robdclark@gmail.com>
Cc: Kristian H. Kristensen <hoegsberg@gmail.com>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Daniel Stone <daniels@collabora.com> (v2)
Reviewed-by: Liviu Dudau <liviu@dudau.co.uk> (v2)
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com> (v3)
Signed-off-by: Daniel Stone <daniels@collabora.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170724034641.13369-2-ben@bwidawsk.net

include/uapi/drm/drm_mode.h

@@ -712,6 +712,56 @@ struct drm_mode_atomic {
 	__u64 user_data;
 };
 
+struct drm_format_modifier_blob {
+#define FORMAT_BLOB_CURRENT 1
+	/* Version of this blob format */
+	u32 version;
+
+	/* Flags */
+	u32 flags;
+
+	/* Number of fourcc formats supported */
+	u32 count_formats;
+
+	/* Where in this blob the formats exist (in bytes) */
+	u32 formats_offset;
+
+	/* Number of drm_format_modifiers */
+	u32 count_modifiers;
+
+	/* Where in this blob the modifiers exist (in bytes) */
+	u32 modifiers_offset;
+
+	/* u32 formats[] */
+	/* struct drm_format_modifier modifiers[] */
+};
+
+struct drm_format_modifier {
+	/* Bitmask of formats in get_plane format list this info applies to. The
+	 * offset allows a sliding window of which 64 formats (bits).
+	 *
+	 * Some examples:
+	 * In today's world with < 65 formats, and formats 0, and 2 are
+	 * supported
+	 * 0x0000000000000005
+	 *		  ^-offset = 0, formats = 5
+	 *
+	 * If the number formats grew to 128, and formats 98-102 are
+	 * supported with the modifier:
+	 *
+	 * 0x0000003c00000000 0000000000000000
+	 *		  ^
+	 *		  |__offset = 64, formats = 0x3c00000000
+	 *
+	 */
+	__u64 formats;
+	__u32 offset;
+	__u32 pad;
+
+	/* The modifier that applies to the >get_plane format list bitmask. */
+	__u64 modifier;
+};
+
 /**
  * Create a new 'blob' data property, copying length bytes from data pointer,
  * and returning new blob ID.