Re: [PATCH] drm/msm/dsi: setup RC model properly

[Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>]

On Fri, Mar 06, 2026 at 05:25:53PM +0800, Pengyu Luo wrote:
> Using incorrect parameters does not seem to affect the display, but we
> should use the correct in accordance with the DSC 1.1 or 1.2.
> 
> Signed-off-by: Pengyu Luo <mitltlatltl@gmail.com>
> ---
>  drivers/gpu/drm/msm/dsi/dsi_host.c | 31 +++++++++++++++++++++++++++---
>  1 file changed, 28 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
> index b60b26ddb0..276c63d2ac 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> @@ -1843,10 +1843,35 @@ static int dsi_populate_dsc_params(struct msm_dsi_host *msm_host, struct drm_dsc
>  	drm_dsc_set_const_params(dsc);
>  	drm_dsc_set_rc_buf_thresh(dsc);
>  
> -	/* DPU supports only pre-SCR panels */
> -	ret = drm_dsc_setup_rc_params(dsc, DRM_DSC_1_1_PRE_SCR);
> +	if (dsc->dsc_version_major != 1) {
> +		DRM_DEV_ERROR(&msm_host->pdev->dev, "Unsupported DSC version: %x.%x\n",
> +			      dsc->dsc_version_major, dsc->dsc_version_minor);
> +		return -EOPNOTSUPP;
> +	}
> +
> +	switch (dsc->dsc_version_minor) {
> +	case 1:
> +		/*
> +		 * For DSC1.1. the upstream lacks SCR parameters, the downstream
> +		 * parameters are unverified here, we support pre-SCR only.

It doesn't. It's the same as DRM_DSC_1_2_444. Please send a patch adding
the comment.

> +		 */
> +		ret = drm_dsc_setup_rc_params(dsc, DRM_DSC_1_1_PRE_SCR);
> +		break;
> +	case 2:
> +		if (dsc->native_422)
> +			ret = drm_dsc_setup_rc_params(dsc, DRM_DSC_1_2_422);
> +		else if (dsc->native_420)
> +			ret = drm_dsc_setup_rc_params(dsc, DRM_DSC_1_2_420);
> +		else

It's not that we support 422/420 output... But yes, it's easier to fix
it now.

> +			ret = drm_dsc_setup_rc_params(dsc, DRM_DSC_1_2_444);
> +		break;
> +	default:
> +		ret = -EOPNOTSUPP;
> +	}
> +
>  	if (ret) {
> -		DRM_DEV_ERROR(&msm_host->pdev->dev, "could not find DSC RC parameters\n");
> +		DRM_DEV_ERROR(&msm_host->pdev->dev, "could not find DSC RC parameters for DSC version: %x.%x\n",
> +			      dsc->dsc_version_major, dsc->dsc_version_minor);
>  		return ret;
>  	}
>  
> -- 
> 2.53.0
> 

-- 
With best wishes
Dmitry