linux-kernel - [PATCH 1/3] drm/fourcc: Add missing big-endian XRGB1555 and RGB565 formats

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Date:   Fri,  8 Jul 2022 20:21:07 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     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>,
        Noralf Trønnes <noralf@...nnes.org>,
        Gerd Hoffmann <kraxel@...hat.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        linux-m68k@...r.kernel.org, linux-kernel@...r.kernel.org,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: [PATCH 1/3] drm/fourcc: Add missing big-endian XRGB1555 and RGB565 formats

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@...ux-m68k.org>
---
Cirrus is the only driver setting quirk_addfb_prefer_host_byte_order
and supporting RGB565 or XRGB1555, but no one tried that on big-endian?
Cirrus does not support DRM_FORMAT_RGB565 | DRM_FORMAT_BIG_ENDIAN
in cirrus_fb_create, so you cannot get a graphical text console.

Do we need these definitions on little-endian platforms, too?
Would it be better to use "DRM_FORMAT_{XRGB1555,RGB565} |
DRM_FORMAT_BIG_ENDIAN" instead of "DRM_FORMAT_HOST_{XRGB1555,RGB565}" in
formats[]?

Alternative, callers could filter out the DRM_FORMAT_BIG_ENDIAN flag
when calling {,__}drm_format_info().

Advantages:
  - No need to have separate entries with DRM_FORMAT_BIG_ENDIAN set.

Disadvantages:
  - {,__}drm_format_info() returns a pointer to a const object,
    whose .format field won't have the DRM_FORMAT_BIG_ENDIAN flag set,
    complicating callers,
  - All callers need to be updated,
  - It is difficult to know which big-endian formats are really
    supported, especially as only a few are needed.
---
 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..16a854c9e07fa4b0 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_HOST_XRGB1555,	.depth = 15, .num_planes = 1, .cpp = { 2, 0, 0 }, .hsub = 1, .vsub = 1 },
+		{ .format = DRM_FORMAT_HOST_RGB565,	.depth = 16, .num_planes = 1, .cpp = { 2, 0, 0 }, .hsub = 1, .vsub = 1 },
+#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 },
-- 
2.25.1