drm/fourcc: Add Arm 16x16 block modifier

Add the DRM_FORMAT_MOD_ARM_16X16_BLOCK_U_INTERLEAVED modifier to
denote the 16x16 block u-interleaved format used in Arm Utgard and
Midgard GPUs.

Changes from v1:-
1. Reserved the upper four bits (out of the 56 bits assigned to each vendor)
to denote the category of Arm specific modifiers. Currently, we have two
categories ie AFBC and MISC.

Changes from v2:-
1. Preserved Ray's authorship
2. Cleanups/changes suggested by Brian
3. Added r-bs of Brian and Qiang

Signed-off-by: Raymond Smith <raymond.smith@arm.com>
Reviewed-by: Brian Starkey <brian.starkey@arm.com>
Reviewed-by: Qiang Yu <yuq825@gmail.com>
Signed-off-by: Ayan kumar halder <ayan.halder@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191004141222.22337-1-ayan.halder@arm.com

include/uapi/drm/drm_fourcc.h

@@ -648,7 +648,21 @@ extern "C" {
  * Further information on the use of AFBC modifiers can be found in
  * Documentation/gpu/afbc.rst
  */
-#define DRM_FORMAT_MOD_ARM_AFBC(__afbc_mode)	fourcc_mod_code(ARM, __afbc_mode)
+
+/*
+ * The top 4 bits (out of the 56 bits alloted for specifying vendor specific
+ * modifiers) denote the category for modifiers. Currently we have only two
+ * categories of modifiers ie AFBC and MISC. We can have a maximum of sixteen
+ * different categories.
+ */
+#define DRM_FORMAT_MOD_ARM_CODE(__type, __val) \
+	fourcc_mod_code(ARM, ((__u64)(__type) << 52) | ((__val) & 0x000fffffffffffffULL))
+
+#define DRM_FORMAT_MOD_ARM_TYPE_AFBC 0x00
+#define DRM_FORMAT_MOD_ARM_TYPE_MISC 0x01
+
+#define DRM_FORMAT_MOD_ARM_AFBC(__afbc_mode) \
+	DRM_FORMAT_MOD_ARM_CODE(DRM_FORMAT_MOD_ARM_TYPE_AFBC, __afbc_mode)
 
 /*
  * AFBC superblock size
@@ -742,6 +756,16 @@ extern "C" {
  */
 #define AFBC_FORMAT_MOD_BCH     (1ULL << 11)
 
+/*
+ * Arm 16x16 Block U-Interleaved modifier
+ *
+ * This is used by Arm Mali Utgard and Midgard GPUs. It divides the image
+ * into 16x16 pixel blocks. Blocks are stored linearly in order, but pixels
+ * in the block are reordered.
+ */
+#define DRM_FORMAT_MOD_ARM_16X16_BLOCK_U_INTERLEAVED \
+	DRM_FORMAT_MOD_ARM_CODE(DRM_FORMAT_MOD_ARM_TYPE_MISC, 1ULL)
+
 /*
  * Allwinner tiled modifier
  *