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SubjectRe: [PATCH resend v2] drm/fourcc: Add missing big-endian XRGB1555 and RGB565 formats
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Hi

Am 23.11.22 um 17:43 schrieb Geert Uytterhoeven:
> As of commit eae06120f1974e1a ("drm: refuse ADDFB2 ioctl for broken
> bigendian drivers"), drivers must set the
> quirk_addfb_prefer_host_byte_order quirk to make the drm_mode_addfb()
> compat code work correctly on big-endian machines.
>
> While that works fine for big-endian XRGB8888 and ARGB8888, which are
> mapped to the existing little-endian BGRX8888 and BGRA8888 formats, it
> does not work for big-endian XRGB1555 and RGB565, as the latter are not
> listed in the format database.
>
> Fix this by adding the missing formats. Limit this to big-endian
> platforms, as there is currently no need to support these formats on
> little-endian platforms.
>
> Fixes: 6960e6da9cec3f66 ("drm: fix drm_mode_addfb() on big endian machines.")
> Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
> ---
> v2:
> - Use "DRM_FORMAT_foo | DRM_FORMAT_BIG_ENDIAN" instead of
> "DRM_FORMAT_HOST_foo",
> - Turn into a lone patch, as all other patches from series
> https://lore.kernel.org/r/cover.1657300532.git.geert@linux-m68k.org
> were applied to drm-misc/for-linux-next.
> ---
> drivers/gpu/drm/drm_fourcc.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_fourcc.c b/drivers/gpu/drm/drm_fourcc.c
> index e09331bb3bc73f21..265671a7f9134c1f 100644
> --- a/drivers/gpu/drm/drm_fourcc.c
> +++ b/drivers/gpu/drm/drm_fourcc.c
> @@ -190,6 +190,10 @@ const struct drm_format_info *__drm_format_info(u32 format)
> { .format = DRM_FORMAT_BGRA5551, .depth = 15, .num_planes = 1, .cpp = { 2, 0, 0 }, .hsub = 1, .vsub = 1, .has_alpha = true },
> { .format = DRM_FORMAT_RGB565, .depth = 16, .num_planes = 1, .cpp = { 2, 0, 0 }, .hsub = 1, .vsub = 1 },
> { .format = DRM_FORMAT_BGR565, .depth = 16, .num_planes = 1, .cpp = { 2, 0, 0 }, .hsub = 1, .vsub = 1 },
> +#ifdef __BIG_ENDIAN
> + { .format = DRM_FORMAT_XRGB1555 | DRM_FORMAT_BIG_ENDIAN, .depth = 15, .num_planes = 1, .cpp = { 2, 0, 0 }, .hsub = 1, .vsub = 1 },
> + { .format = DRM_FORMAT_RGB565 | DRM_FORMAT_BIG_ENDIAN, .depth = 16, .num_planes = 1, .cpp = { 2, 0, 0 }, .hsub = 1, .vsub = 1 },

Getting back to the discussion on endianess, I don't understand why the
BIG_ENDIAN flag is set here. AFAIK these formats are always little
endian. And the BE flag is set by drivers/userspace if a framebuffer
has a BE ordering.

It would be better to filter the BE flag in __drm_format_info() before
the function does the lookup.

Best regards
Thomas

> +#endif
> { .format = DRM_FORMAT_RGB888, .depth = 24, .num_planes = 1, .cpp = { 3, 0, 0 }, .hsub = 1, .vsub = 1 },
> { .format = DRM_FORMAT_BGR888, .depth = 24, .num_planes = 1, .cpp = { 3, 0, 0 }, .hsub = 1, .vsub = 1 },
> { .format = DRM_FORMAT_XRGB8888, .depth = 24, .num_planes = 1, .cpp = { 4, 0, 0 }, .hsub = 1, .vsub = 1 },

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev
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