Re: [PATCH 3/3] drm/msm/dpu: fix video mode DSC INTF timing width for non 8 bit panels

[Dmitry Baryshkov]

On Wed, Mar 18, 2026 at 09:41:09AM +0000, Alexander Koskovich wrote:
> Using bits_per_component * 3 as the divisor for the compressed INTF
> timing width produces constant FIFO errors for panels such as the BOE
> BF068MWM-TD0 which is a 10 bit panel.
> 
> The downstream driver calculates the compressed timing width by
> dividing the total compressed bytes per line by 3 which does not depend
> on bits_per_component. Switch the divisor to 24 to match downstream.
> 
> Signed-off-by: Alexander Koskovich <akoskovich@xxxxx>
> ---
>  drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c
> index 0ba777bda253..9b046a0e77aa 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c
> @@ -122,19 +122,21 @@ static void drm_mode_to_intf_timing_params(
>  	}
>  
>  	/*
> -	 * for DSI, if compression is enabled, then divide the horizonal active
> -	 * timing parameters by compression ratio. bits of 3 components(R/G/B)
> -	 * is compressed into bits of 1 pixel.
> +	 * For DSI, if DSC is enabled, use a fixed divisor of 24 rather than
> +	 * bits_per_component * 3 when calculating the compressed timing width.
> +	 *
> +	 * This matches the downstream driver and is required for panels with
> +	 * bits_per_component != 8.
>  	 */
>  	if (phys_enc->hw_intf->cap->type != INTF_DP && timing->compression_en) {
>  		struct drm_dsc_config *dsc =
>  		       dpu_encoder_get_dsc_config(phys_enc->parent);
> +
>  		/*
>  		 * TODO: replace drm_dsc_get_bpp_int with logic to handle
>  		 * fractional part if there is fraction
>  		 */
> -		timing->width = timing->width * drm_dsc_get_bpp_int(dsc) /
> -				(dsc->bits_per_component * 3);
> +		timing->width = timing->width * drm_dsc_get_bpp_int(dsc) / 24;
>  		timing->xres = timing->width;
>  	}
>  }

It's already a third patch touching this part of code. I hope Marijn can
comment here.

-- 
With best wishes
Dmitry