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

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Date: Thu, 27 Jun 2024 19:35:30 +0200
From: Thomas Huth <thuth@...hat.com>
To: 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,
	Javier Martinez Canillas <javierm@...hat.com>,
	Hamza Mahfooz <hamza.mahfooz@....com>
Subject: [PATCH] drm/fbdev-generic: Fix framebuffer on big endian devices

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))
-- 
2.45.2