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Date:   Thu, 17 Feb 2022 15:35:08 +0100
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Subject: Re: [PATCH 8/8] drm/fourcc: Add DRM_FORMAT_D1
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To:     Pekka Paalanen <ppaalanen@gmail.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>
Cc:     Linux Fbdev development list <linux-fbdev@vger.kernel.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        David Airlie <airlied@linux.ie>, Helge Deller <deller@gmx.de>,
        Javier Martinez Canillas <javierm@redhat.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux/m68k <linux-m68k@vger.kernel.org>,
        DRI Development <dri-devel@lists.freedesktop.org>
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From:   =?UTF-8?Q?Michel_D=c3=a4nzer?= <michel.daenzer@mailbox.org>
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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