Re: [PATCH 8/8] drm/fourcc: Add DRM_FORMAT_D1

Michel Dänzer
2022-02-17T14:35:25Z

On 2022-02-17 15:28, Pekka Paalanen wrote:
> On Thu, 17 Feb 2022 11:42:29 +0100
> Geert Uytterhoeven <geert@linux-m68k.org> wrote:
>
>> Hi Pekka,
>>
>> On Thu, Feb 17, 2022 at 11:10 AM Pekka Paalanen <ppaalanen@gmail.com> wrote:
>>> On Tue, 15 Feb 2022 17:52:26 +0100
>>> Geert Uytterhoeven <geert@linux-m68k.org> wrote:
>>>> Introduce a fourcc code for a single-channel frame buffer format with two
>>>> darkness levels. This can be used for two-level dark-on-light displays.
>>>>
>>>> As the number of bits per pixel is less than eight, this relies on
>>>> proper block handling for the calculation of bits per pixel and pitch.
>>>>
>>>> Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
>>
>>>> --- a/drivers/gpu/drm/drm_fourcc.c
>>>> +++ b/drivers/gpu/drm/drm_fourcc.c
>>>> @@ -151,6 +151,8 @@ 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_D1, .depth = 1, .num_planes = 1,
>>>> + .char_per_block = { 1, }, .block_w = { 8, }, .block_h = { 1, }, .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 8605a1acc6813e6c..c15c6efcc65e5827 100644
>>>> --- a/include/uapi/drm/drm_fourcc.h
>>>> +++ b/include/uapi/drm/drm_fourcc.h
>>>> @@ -104,6 +104,9 @@ 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 Darkness */
>>>> +#define DRM_FORMAT_D1 fourcc_code('D', '1', ' ', ' ') /* [0] D */
>>>> +
>>>
>>> the same comment here as for C1 and R1 formats, need to specify pixel
>>> ordering inside a byte.
>>
>> Right, will do.
>
> Btw. does endianess of anything have any effect on these pixel formats?
>
> That's probably a weird question, but I recall Pixman (the pixel
> handling library of the X server nowadays known as Xorg) having pixel
> formats where CPU endianess affects whether the first pixel in a byte
> is found at the MSB or LSB.

Pixman probably has that for hysterical raisins inherited from the X code base. Conceptually, endianness is purely about the order of bytes in words, and is orthogonal to the order in which the bits of a byte/word are numbered.

--
Earthling Michel Dänzer | https://redhat.com
Libre software enthusiast | Mesa and Xwayland developer