Hi Michel,
On Mon, Jul 11, 2022 at 5:23 PM Michel Dänzer
<michel.daenzer@xxxxxxxxxxx> wrote:
On 2022-07-08 20:21, Geert Uytterhoeven wrote:
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@xxxxxxxxxxxxxx>
---
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[]?
The intention of DRM_FORMAT_HOST_* is that they are macros in include/drm/drm_fourcc.h which just map to little endian formats defined in drivers/gpu/drm/drm_fourcc.c. Since this is not possible for big endian hosts for XRGB1555 or RGB565 (or any other format with non-8-bit components), this isn't applicable here.
I read that as that you prefer to write
"DRM_FORMAT_{XRGB1555,RGB565} | DRM_FORMAT_BIG_ENDIAN" in formats[]?
It's also doubtful that Cirrus hardware would access these formats as big endian (drivers/gpu/drm/tiny/cirrus.c has no endianness references at all, and the hardware was surely designed for x86 first and foremost).
Instead, fbcon (and user space) needs to convert to little endian when using DRM_FORMAT_HOST_{XRGB1555,RGB565} with the cirrus driver on big endian hosts.
Yeah, probably the cirrus driver can use some fixes...
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
