linux-kernel - Re: [PATCH 7/8] drm/fourcc: Add DRM_FORMAT

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Date:   Thu, 17 Feb 2022 12:02:58 +0200
From:   Pekka Paalanen <ppaalanen@...il.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, Helge Deller <deller@....de>,
        Javier Martinez Canillas <javierm@...hat.com>,
        linux-fbdev@...r.kernel.org, linux-m68k@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/8] drm/fourcc: Add DRM_FORMAT_R[124]

On Tue, 15 Feb 2022 17:52:25 +0100
Geert Uytterhoeven <geert@...ux-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@...ux-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

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