[7/8] drm/fourcc: Add DRM_FORMAT_R[124]

Introduce fourcc codes for single-channel frame buffer formats with two,
four, and sixteen intensity levels.  Traditionally, the first channel
has been called the "red" channel, but the fourcc can also be used for
other light-on-dark displays.

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

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
---
 drivers/gpu/drm/drm_fourcc.c  | 6 ++++++
 include/uapi/drm/drm_fourcc.h | 9 +++++++++
 2 files changed, 15 insertions(+)

On Tue, 15 Feb 2022 17:52:25 +0100
Geert Uytterhoeven <geert@linux-m68k.org> wrote:

> Introduce fourcc codes for single-channel frame buffer formats with two,
> four, and sixteen intensity levels.  Traditionally, the first channel
> has been called the "red" channel, but the fourcc can also be used for
> other light-on-dark displays.
> 
> As the number of bits per pixel is less than eight, these rely on proper
> block handling for the calculation of bits per pixel and pitch.
> 
> Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
> ---
>  drivers/gpu/drm/drm_fourcc.c  | 6 ++++++
>  include/uapi/drm/drm_fourcc.h | 9 +++++++++
>  2 files changed, 15 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_fourcc.c b/drivers/gpu/drm/drm_fourcc.c
> index 5c77ce10f53e3a64..c12e48ecb1ab8aad 100644
> --- a/drivers/gpu/drm/drm_fourcc.c
> +++ b/drivers/gpu/drm/drm_fourcc.c
> @@ -151,6 +151,12 @@ 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 },
>  		{ .format = DRM_FORMAT_C8,		.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,
> +		  .char_per_block = { 1, }, .block_w = { 4, }, .block_h = { 1, }, .hsub = 1, .vsub = 1 },
> +		{ .format = DRM_FORMAT_R4,		.depth = 4,  .num_planes = 1,
> +		  .char_per_block = { 1, }, .block_w = { 2, }, .block_h = { 1, }, .hsub = 1, .vsub = 1 },
>  		{ .format = DRM_FORMAT_R8,		.depth = 8,  .num_planes = 1, .cpp = { 1, 0, 0 }, .hsub = 1, .vsub = 1 },
>  		{ .format = DRM_FORMAT_R10,		.depth = 10, .num_planes = 1, .cpp = { 2, 0, 0 }, .hsub = 1, .vsub = 1 },
>  		{ .format = DRM_FORMAT_R12,		.depth = 12, .num_planes = 1, .cpp = { 2, 0, 0 }, .hsub = 1, .vsub = 1 },
> diff --git a/include/uapi/drm/drm_fourcc.h b/include/uapi/drm/drm_fourcc.h
> index 3f09174670b3cce6..8605a1acc6813e6c 100644
> --- a/include/uapi/drm/drm_fourcc.h
> +++ b/include/uapi/drm/drm_fourcc.h
> @@ -104,6 +104,15 @@ extern "C" {
>  #define DRM_FORMAT_C4		fourcc_code('C', '4', ' ', ' ') /* [3:0] C */
>  #define DRM_FORMAT_C8		fourcc_code('C', '8', ' ', ' ') /* [7:0] C */
>  
> +/* 1 bpp Red */
> +#define DRM_FORMAT_R1		fourcc_code('R', '1', ' ', ' ') /* [0] R */
> +
> +/* 2 bpp Red */
> +#define DRM_FORMAT_R2		fourcc_code('R', '2', ' ', ' ') /* [1:0] R */
> +
> +/* 4 bpp Red */
> +#define DRM_FORMAT_R4		fourcc_code('R', '4', ' ', ' ') /* [3:0] R */
> +
>  /* 8 bpp Red */
>  #define DRM_FORMAT_R8		fourcc_code('R', '8', ' ', ' ') /* [7:0] R */
>  

Hi Geert,

I have the same comment here as for C1/C2/C4: these need to specify the
ordering inside a byte. Otherwise this reads as one byte of storage per
pixel, but using only 1/2/4 bits of each byte.

The idea of having Cx and Rx formats separately sounds good to me.


Thanks,
pq