[Intel-gfx] [PATCH v3] drm/i915/xelpd: Calculate first_line_bpg_offset for DSC 1.1

[Kandpal, Suraj]

> This change is required for DSC 1.1 because the current calculation is for DSC
> 1.2 and may get a calculated value which is not recommended by DSC 1.1, for
> example, the calculated value at 8bpp becomes 15, not the value of 12
> recommened by DSC 1.1.
> 

Hi Tseng,
Please find the comments below

> v2:
> - change the if-condition from minor version 2 to 1.
> - add comment about first_line_bpg_offset for DSC 1.1.
> v3:
> - change variable name from rc to vdsc_cfg.
> - add Cc
> 
> Cc: Suraj Kandpal <suraj.kandpal at intel.com>
> Cc: Ankit Nautiyal <ankit.k.nautiyal at intel.com>
> Cc: Juha-Pekka Heikkil <juha-pekka.heikkila at intel.com>
> Signed-off-by: William Tseng <william.tseng at intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_vdsc.c | 18 +++++++++++++-----
>  1 file changed, 13 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_vdsc.c
> b/drivers/gpu/drm/i915/display/intel_vdsc.c
> index bd9116d2cd76..c7db3bc94246 100644
> --- a/drivers/gpu/drm/i915/display/intel_vdsc.c
> +++ b/drivers/gpu/drm/i915/display/intel_vdsc.c
> @@ -72,11 +72,19 @@ calculate_rc_params(struct drm_dsc_config
> *vdsc_cfg)
>  	int qp_bpc_modifier = (bpc - 8) * 2;
>  	u32 res, buf_i, bpp_i;
> 
> -	if (vdsc_cfg->slice_height >= 8)
> -		vdsc_cfg->first_line_bpg_offset =
> -			12 + DIV_ROUND_UP((9 * min(34, vdsc_cfg-
> >slice_height - 8)), 100);
> -	else
> -		vdsc_cfg->first_line_bpg_offset = 2 * (vdsc_cfg->slice_height -
> 1);
> +	if (vdsc_cfg->dsc_version_minor == 1) {
> +		/* The recommended and required Values from Table E-2 for
> DSC1.1 */
> +		if (bpp == 8)
> +			vdsc_cfg->first_line_bpg_offset = 12;
> +		else
> +			vdsc_cfg->first_line_bpg_offset = 15;
> +	} 

This code block wont be needed check comment below

else {
> +		if (vdsc_cfg->slice_height >= 8)
> +			vdsc_cfg->first_line_bpg_offset =
> +				12 + DIV_ROUND_UP((9 * min(34, vdsc_cfg-
> >slice_height - 8)), 100);

I think you missed the comment from Ankit but if you check the Errata of DSC 1.1 they remove the ask for using 12 as
first_line_bpg_offset when bpp is 8 and use the formula 
first_line_bpg_offset = 12 + floor(0.09 * MIN (34, slice_height - 8))for slice_height ≥ 8
which currently is incorrect as we are using DIV_ROUND_UP.
Your issue should be solved if you replace DIV_ROUND_UP with floor or a simple typecast.

Regards,
Suraj Kandpal

> +		else
> +			vdsc_cfg->first_line_bpg_offset = 2 * (vdsc_cfg-
> >slice_height - 1);
> +	}
> 
>  	/* Our hw supports only 444 modes as of today */
>  	if (bpp >= 12)
> --
> 2.34.1