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

[David Lechner]

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")
Signed-off-by: David Lechner <dlechner@xxxxxxxxxxxx>
---
 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 b57ebf37a664..16b6b4e368af 100644
--- a/drivers/gpu/drm/sitronix/st7586.c
+++ b/drivers/gpu/drm/sitronix/st7586.c
@@ -347,6 +347,12 @@ 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;
 
@@ -356,15 +362,6 @@ 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);

---
base-commit: 3fa5e5702a82d259897bd7e209469bc06368bf31
change-id: 20260228-drm-mipi-dbi-fix-st7586-byte-swap-f0d03c5f800c

Best regards,
-- 
David Lechner <dlechner@xxxxxxxxxxxx>