[PATCH v2] drm/tiny: panel-mipi-dbi: Use drm_client_setup_with_fourcc()

[Fabio Estevam <festevam@gmail.com>]

From: Fabio Estevam <festevam@denx.de>

Since commit 559358282e5b ("drm/fb-helper: Don't use the preferred depth
for the BPP default"), RGB565 displays such as the CFAF240320X no longer
render correctly: colors are distorted and the content is shown twice
horizontally.

This regression is due to the fbdev emulation layer defaulting to 32 bits
per pixel, whereas the display expects 16 bpp (RGB565). As a result, the
framebuffer data is incorrectly interpreted by the panel.

Fix the issue by calling drm_client_setup_with_fourcc() with a format
explicitly selected based on the display's bits-per-pixel value. For 16
bpp, use DRM_FORMAT_RGB565; for other values, fall back to the previous
behavior. This ensures that the allocated framebuffer format matches the
hardware expectations, avoiding color and layout corruption.

Tested on a CFAF240320X display with an RGB565 configuration, confirming
correct colors and layout after applying this patch.

Cc: stable@vger.kernel.org
Fixes: 559358282e5b ("drm/fb-helper: Don't use the preferred depth for the BPP default")
Signed-off-by: Fabio Estevam <festevam@denx.de>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
---
Changes since v1:
- Improved the commit log.
- Added Thomas' Reviewed-by tag.
- Added more maintainers on Cc as panel-mipi-dbi.c has been marked as orphan.

 drivers/gpu/drm/tiny/panel-mipi-dbi.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/tiny/panel-mipi-dbi.c b/drivers/gpu/drm/tiny/panel-mipi-dbi.c
index 0460ecaef4bd..23914a9f7fd3 100644
--- a/drivers/gpu/drm/tiny/panel-mipi-dbi.c
+++ b/drivers/gpu/drm/tiny/panel-mipi-dbi.c
@@ -390,7 +390,10 @@ static int panel_mipi_dbi_spi_probe(struct spi_device *spi)
 
 	spi_set_drvdata(spi, drm);
 
-	drm_client_setup(drm, NULL);
+	if (bpp == 16)
+		drm_client_setup_with_fourcc(drm, DRM_FORMAT_RGB565);
+	else
+		drm_client_setup_with_fourcc(drm, DRM_FORMAT_RGB888);
 
 	return 0;
 }
-- 
2.34.1