linux-kernel - Re: [PATCH] drm/fbdev-generic: Fix framebuffer on big endian devices

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Date: Mon, 1 Jul 2024 10:54:29 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Thomas Huth <thuth@...hat.com>
Cc: Thomas Zimmermann <tzimmermann@...e.de>, dri-devel@...ts.freedesktop.org, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, linux-kernel@...r.kernel.org, 
	Javier Martinez Canillas <javierm@...hat.com>, Hamza Mahfooz <hamza.mahfooz@....com>
Subject: Re: [PATCH] drm/fbdev-generic: Fix framebuffer on big endian devices

Hi Thomas,

On Mon, Jul 1, 2024 at 10:42 AM Thomas Huth <thuth@...hat.com> wrote:
> On 28/06/2024 08.07, Thomas Zimmermann wrote:
> > Am 27.06.24 um 19:35 schrieb Thomas Huth:
> >> Starting with kernel 6.7, the framebuffer text console is not working
> >> anymore with the virtio-gpu device on s390x hosts. Such big endian fb
> >> devices are usinga different pixel ordering than little endian devices,
> >> e.g. DRM_FORMAT_BGRX8888 instead of DRM_FORMAT_XRGB8888.
> >>
> >> This used to work fine as long as drm_client_buffer_addfb() was still
> >> calling drm_mode_addfb() which called drm_driver_legacy_fb_format()
> >> internally to get the right format. But drm_client_buffer_addfb() has
> >> recently been reworked to call drm_mode_addfb2() instead with the
> >> format value that has been passed to it as a parameter (see commit
> >> 6ae2ff23aa43 ("drm/client: Convert drm_client_buffer_addfb() to
> >> drm_mode_addfb2()").
> >>
> >> That format parameter is determined in drm_fbdev_generic_helper_fb_probe()
> >> via the drm_mode_legacy_fb_format() function - which only generates
> >> formats suitable for little endian devices. So to fix this issue
> >> switch to drm_driver_legacy_fb_format() here instead to take the
> >> device endianness into consideration.
> >>
> >> Fixes: 6ae2ff23aa43 ("drm/client: Convert drm_client_buffer_addfb() to
> >> drm_mode_addfb2()")
> >> Closes: https://issues.redhat.com/browse/RHEL-45158
> >> Signed-off-by: Thomas Huth <thuth@...hat.com>
> >
> > Acked-by: Thomas Zimmermann <tzimmermann@...e.de>
> >
> >
> >> ---
> >>   drivers/gpu/drm/drm_fbdev_generic.c | 3 ++-
> >
> > This file is now called drm_fbdev_ttm.c in drm-misc-next.
>
> Oh, ok, shall I send a v2 that is adjusted to that change, or can it be
> fixed while applying my patch?

As this is a regression in mainline, which needs to be backported,
too, it's best to apply your fix to v6.10-rc6, which does not have
drm_fbdev_ttm.c yet.

> > And a similar patch might be necessary for drm_fbdev_dma.c.
>
> Looks similar, indeed. Shall I send a patch for that one, too? ... I
> currently don't have a setup for testing that, though...

Obviously these need to be fixed, too.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

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