Re: [PATCH v3 4/4] drm/msm/dpu: fix video mode DSC INTF timing width calculation

[Neil Armstrong <neil.armstrong@linaro.org>]

Hi,

On 3/19/26 12:58, Alexander Koskovich wrote:
> Using bits_per_component * 3 as the divisor for the compressed INTF
> timing width produces constant FIFO errors for the BOE BF068MWM-TD0
> panel due to bits_per_component being 10 which results in a divisor
> of 30 instead of 24.
> 
> Regardless of the compression ratio and pixel depth, 24 bits of
> compressed data are transferred per pclk, so the divisor should
> always be 24.

Not true with widebus, specify why 24 and because DSI widebus is not implemented yet.

> 
> Signed-off-by: Alexander Koskovich <akoskovich@pm.me>
> ---
>   drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c | 9 ++++-----
>   1 file changed, 4 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..5419ef0be137 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 +122,18 @@ 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, 24 bits of compressed data are
> +	 * transferred per pclk regardless of the source pixel depth.
>   	 */
>   	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);
> +
Drop this change

>   		/*
>   		 * 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;

It would be helpful to somehow show that 24 is 8 * 3, 8 being the byte width and 3 the compression ratio.

>   		timing->xres = timing->width;
>   	}
>   }
>