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

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Date: Thu, 27 Jun 2024 19:42:26 +0200
From: Javier Martinez Canillas <javierm@...hat.com>
To: Thomas Huth <thuth@...hat.com>, dri-devel@...ts.freedesktop.org, Maarten
 Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard
 <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, David
 Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, Geert
 Uytterhoeven <geert@...ux-m68k.org>
Cc: linux-kernel@...r.kernel.org, Hamza Mahfooz <hamza.mahfooz@....com>
Subject: Re: [PATCH] drm/fbdev-generic: Fix framebuffer on big endian devices

Thomas Huth <thuth@...hat.com> writes:

Hello Thomas,

> 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>
> ---
>  drivers/gpu/drm/drm_fbdev_generic.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_fbdev_generic.c b/drivers/gpu/drm/drm_fbdev_generic.c
> index 97e579c33d84..1e200d815e1a 100644
> --- a/drivers/gpu/drm/drm_fbdev_generic.c
> +++ b/drivers/gpu/drm/drm_fbdev_generic.c
> @@ -84,7 +84,8 @@ static int drm_fbdev_generic_helper_fb_probe(struct drm_fb_helper *fb_helper,
>  		    sizes->surface_width, sizes->surface_height,
>  		    sizes->surface_bpp);
>  
> -	format = drm_mode_legacy_fb_format(sizes->surface_bpp, sizes->surface_depth);
> +	format = drm_driver_legacy_fb_format(dev, sizes->surface_bpp,
> +					     sizes->surface_depth);
>  	buffer = drm_client_framebuffer_create(client, sizes->surface_width,
>  					       sizes->surface_height, format);
>  	if (IS_ERR(buffer))

Indeed. Thanks a lot for the detailed explanation and the patch.
Your fix makes sense to me.

Reviewed-by: Javier Martinez Canillas <javierm@...hat.com>

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat