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

[Tseng, William]

Thank you for the comments.  I have made the corresponding changes to the revised patch in version No.3.

-----Original Message-----
From: Kandpal, Suraj <suraj.kandpal at intel.com> 
Sent: Wednesday, August 2, 2023 7:15 PM
To: Tseng, William <william.tseng at intel.com>; intel-gfx at lists.freedesktop.org
Cc: Heikkila, Juha-pekka <juha-pekka.heikkila at intel.com>; Tseng, William <william.tseng at intel.com>; Nautiyal, Ankit K <ankit.k.nautiyal at intel.com>
Subject: RE: [Intel-gfx] [PATCH] drm/i915/xelpd: Calculate first_line_bpg_offset for DSC 1.1

1.1
> 
> 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.
> 
> 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 | 17 ++++++++++++-----
>  1 file changed, 12 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..9b350f5f8ebb 100644
> --- a/drivers/gpu/drm/i915/display/intel_vdsc.c
> +++ b/drivers/gpu/drm/i915/display/intel_vdsc.c
> @@ -72,11 +72,18 @@ 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 == 2) {

I think the check here should be for minor version 1 and move the code in this block to the else block and vice versa as this 8 bpp corner case is applicable only to DSC 1.1
 
> +		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);
> +	} else {
> +		if (bpp == 8)
> +			rc->first_line_bpg_offset = 12;
> +		else
> +			rc->first_line_bpg_offset = 15;
> +	}

Add the section in DSC spec/ Cmodel from where one can verify this in comments

Regards,
Suraj Kandpal
> 
>  	/* Our hw supports only 444 modes as of today */
>  	if (bpp >= 12)
> --
> 2.34.1