Hi,
thanks for the bug report.
Am 16.04.25 um 04:23 schrieb Fabio Estevam:
Hi,
I have a custom board populated with a cfaf240320x panel connected via
SPI and driven by the drivers/gpu/drm/tiny/panel-mipi-dbi.c driver.
It works well on kernel 6.1.
After upgrading the kernel to 6.12 (also tested Linux-next), the panel
no longer works correctly: the colors are wrong, and the image appears
twice, one in each half of the screen.
Running git bisect pointed to the following bad commit:
559358282e5b43b1b01e7f6afac6e0beb33cb4a2 is the first bad commit
commit 559358282e5b43b1b01e7f6afac6e0beb33cb4a2
Author: Thomas Zimmermann <[email protected]>
Date: Wed Nov 23 12:53:48 2022 +0100
drm/fb-helper: Don't use the preferred depth for the BPP default
If no preferred value for bits-per-pixel has been given, fall back
to 32. Never use the preferred depth. The color depth is the number
of color/alpha bits per pixel, while bpp is the overall number of
bits in most cases.
Most noteworthy, XRGB8888 has a depth of 24 and a bpp value of 32.
Using depth for bpp would make the value 24 as well and format
selection in fbdev helpers fails. Unfortunately XRGB8888 is the most
common format and the old heuristic therefore fails for most of
the drivers (unless they implement the 24-bit RGB888 format).
Picking a bpp of 32 will later on result in a default depth of 24
and the format XRGB8888. As XRGB8888 is the default format for most
of the current and legacy graphics stack, all drivers must support
it. So it is the safe choice.
v2:
* fix commit-message typo (Javier)
Signed-off-by: Thomas Zimmermann <[email protected]>
Reviewed-by: Javier Martinez Canillas <[email protected]>
Acked-by: Daniel Vetter <[email protected]>
Link:
https://patchwork.freedesktop.org/patch/msgid/[email protected]
Then I did a quick hack like this:
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -425,7 +425,7 @@ void drm_fb_helper_prepare(struct drm_device *dev,
struct drm_fb_helper *helper,
* format.
*/
if (!preferred_bpp)
- preferred_bpp = 32;
+ preferred_bpp = 16;
INIT_LIST_HEAD(&helper->kernel_fb_list);
spin_lock_init(&helper->damage_lock);
and the display correctly again.
What is the proper fix for this issue?
The proper fix would patch the driver to support 32-bit correctly. It
looks like the panel only supports 16 bpp and 24 bpp, so format
conversion would be required.
For an easier fix, you can replace drm_client_setup() at [1] with
drm_client_setup_with_fourcc() and pass DRM_FORMAT_RGB565 as the second
argument.
Best regards
Thomas
[1]
https://elixir.bootlin.com/linux/v6.13.7/source/drivers/gpu/drm/tiny/panel-mipi-dbi.c#L393
Thanks,
Fabio Estevam
--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)
