[PATCH 6.18 049/333] drm/sitronix/st7586: fix bad pixel data due to byte swap

Greg Kroah-Hartman
2026-03-17T17:07:36Z

From: David Lechner <dlechner@baylibre.com>

[ Upstream commit 46d8a07b4ae262e2fec6ce2aa454e06243661265 ]

Correctly set dbi->write_memory_bpw for the ST7586 driver. This driver
is for a monochrome display that has an unusual data format, so the
default value set in mipi_dbi_spi_init() is not correct simply because
this controller is non-standard.

Previously, we were using dbi->swap_bytes to make the same sort of
workaround, but it was removed in the same commit that added
dbi->write_memory_bpw, so we need to use the latter now to have the
correct behavior.

This fixes every 3 columns of pixels being swapped on the display. There
are 3 pixels per byte, so the byte swap caused this effect.

Fixes: df3fb27a74a4 ("drm/mipi-dbi: Make bits per word configurable for pixel transfers")
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://patch.msgid.link/20260228-drm-mipi-dbi-fix-st7586-byte-swap-v1-1-e78f6c24cd28@baylibre.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/gpu/drm/sitronix/st7586.c | 15 ++++++---------
1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/sitronix/st7586.c b/drivers/gpu/drm/sitronix/st7586.c
index a29672d84eded..055383497aae7 100644
--- a/drivers/gpu/drm/sitronix/st7586.c
+++ b/drivers/gpu/drm/sitronix/st7586.c
@@ -346,6 +346,12 @@ static int st7586_probe(struct spi_device *spi)
if (ret)
return ret;

+ /*
+ * Override value set by mipi_dbi_spi_init(). This driver is a bit
+ * non-standard, so best to set it explicitly here.
+ */
+ dbi->write_memory_bpw = 8;
+
/* Cannot read from this controller via SPI */
dbi->read_commands = NULL;

@@ -355,15 +361,6 @@ static int st7586_probe(struct spi_device *spi)
if (ret)
return ret;

- /*
- * we are using 8-bit data, so we are not actually swapping anything,
- * but setting mipi->swap_bytes makes mipi_dbi_typec3_command() do the
- * right thing and not use 16-bit transfers (which results in swapped
- * bytes on little-endian systems and causes out of order data to be
- * sent to the display).
- */
- dbi->swap_bytes = true;
-
drm_mode_config_reset(drm);

ret = drm_dev_register(drm, 0);
--
2.51.0