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

[Thomas Zimmermann <tzimmermann@suse.de>]

cc Javier

Am 01.03.26 um 05:30 schrieb 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@baylibre.com>
> ---
>   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,

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)