[PATCH/RFC v3 10/10] drm/fourcc: Add DRM_FORMAT_D[1248]

Geert Uytterhoeven
2022-07-08T18:21:36Z

As Rn covers single-channel formats with a direct relationship between
channel value and brightness, and Cn can be any colors, there are
currently no fourcc codes to describe single-channel formats with an
inverse relationship between channel value and brightness.

Introduce fourcc codes for a single-channel frame buffer format with
two, four, sixteen, or 256 brightness ("darkness") levels, where there
is an inverse relationship between channel value and brightness.

As the number of bits per pixel may be less than eight, some of these
formats rely on proper block handling for the calculation of bits per
pixel and pitch.

The fill order (the order in which multiple pixels are packed in a byte)
is the same order as used for grayscale (2, 4, and 16 levels) images in
the PNG specification, Version 1.2.
This order is also the recommended and default order (FillOrder = 1) for
bilevel and grayscale (16 levels) images in the TIFF 6.0 Specification,
and is also used for monochrome images in the PBM file format,
monochrome Linux frame buffer logos, and BDF and PSF (Linux kernel) font
files.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
---
RFC, as I have no immediate need for these formats.

v3:
- Add Reviewed-by,
- Document fill order,
- Replace light-on-dark/dark-on-light by direct/inverse relationship
between channel value and brightness,

v2:
- Add rationale for adding new formats,
- Improve pixel description,
- Add D[248] for completeness.
---
drivers/gpu/drm/drm_fourcc.c | 7 +++++++
include/uapi/drm/drm_fourcc.h | 12 ++++++++++++
2 files changed, 19 insertions(+)

diff --git a/drivers/gpu/drm/drm_fourcc.c b/drivers/gpu/drm/drm_fourcc.c
index 05e65e9ab0c69c6a..e09331bb3bc73f21 100644
--- a/drivers/gpu/drm/drm_fourcc.c
+++ b/drivers/gpu/drm/drm_fourcc.c
@@ -154,6 +154,13 @@ const struct drm_format_info *__drm_format_info(u32 format)
{ .format = DRM_FORMAT_C4, .depth = 4, .num_planes = 1,
.char_per_block = { 1, }, .block_w = { 2, }, .block_h = { 1, }, .hsub = 1, .vsub = 1, .is_color_indexed = true },
{ .format = DRM_FORMAT_C8, .depth = 8, .num_planes = 1, .cpp = { 1, 0, 0 }, .hsub = 1, .vsub = 1, .is_color_indexed = true },
+ { .format = DRM_FORMAT_D1, .depth = 1, .num_planes = 1,
+ .char_per_block = { 1, }, .block_w = { 8, }, .block_h = { 1, }, .hsub = 1, .vsub = 1 },
+ { .format = DRM_FORMAT_D2, .depth = 2, .num_planes = 1,
+ .char_per_block = { 1, }, .block_w = { 4, }, .block_h = { 1, }, .hsub = 1, .vsub = 1 },
+ { .format = DRM_FORMAT_D4, .depth = 4, .num_planes = 1,
+ .char_per_block = { 1, }, .block_w = { 2, }, .block_h = { 1, }, .hsub = 1, .vsub = 1 },
+ { .format = DRM_FORMAT_D8, .depth = 8, .num_planes = 1, .cpp = { 1, 0, 0 }, .hsub = 1, .vsub = 1 },
{ .format = DRM_FORMAT_R1, .depth = 1, .num_planes = 1,
.char_per_block = { 1, }, .block_w = { 8, }, .block_h = { 1, }, .hsub = 1, .vsub = 1 },
{ .format = DRM_FORMAT_R2, .depth = 2, .num_planes = 1,
diff --git a/include/uapi/drm/drm_fourcc.h b/include/uapi/drm/drm_fourcc.h
index 6db4f195d6a15129..7eff27eca7ce707f 100644
--- a/include/uapi/drm/drm_fourcc.h
+++ b/include/uapi/drm/drm_fourcc.h
@@ -104,6 +104,18 @@ extern "C" {
#define DRM_FORMAT_C4 fourcc_code('C', '4', ' ', ' ') /* [7:0] C0:C1 4:4 two pixels/byte */
#define DRM_FORMAT_C8 fourcc_code('C', '8', ' ', ' ') /* [7:0] C */

+/* 1 bpp Darkness (inverse relationship between channel value and brightness) */
+#define DRM_FORMAT_D1 fourcc_code('D', '1', ' ', ' ') /* [7:0] D0:D1:D2:D3:D4:D5:D6:D7 1:1:1:1:1:1:1:1 eight pixels/byte */
+
+/* 2 bpp Darkness (inverse relationship between channel value and brightness) */
+#define DRM_FORMAT_D2 fourcc_code('D', '2', ' ', ' ') /* [7:0] D0:D1:D2:D3 2:2:2:2 four pixels/byte */
+
+/* 4 bpp Darkness (inverse relationship between channel value and brightness) */
+#define DRM_FORMAT_D4 fourcc_code('D', '4', ' ', ' ') /* [7:0] D0:D1 4:4 two pixels/byte */
+
+/* 8 bpp Darkness (inverse relationship between channel value and brightness) */
+#define DRM_FORMAT_D8 fourcc_code('D', '8', ' ', ' ') /* [7:0] D */
+
/* 1 bpp Red (direct relationship between channel value and brightness) */
#define DRM_FORMAT_R1 fourcc_code('R', '1', ' ', ' ') /* [7:0] R0:R1:R2:R3:R4:R5:R6:R7 1:1:1:1:1:1:1:1 eight pixels/byte */

--
2.25.1