Re: [PATCH] drm/i915/dp: Correct max compressed bpp bounds by using link bpp

[Imre Deak <imre.deak@intel.com>]

On Thu, Jan 16, 2025 at 03:24:16PM +0530, Ankit Nautiyal wrote:
> While setting the bounds for compressed bpp we ensure that the
> compressed bpp is less than the pipe bpp.
> 
> This gives an issue with 420 output format where effective link bpp is
> half that of the pipe bpp. Therefore instead of pipe bpp use link bpp to
> set the bounds for the compressed bpp.
> 
> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 1ad25c37f3c2..47fcfbcb893b 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -2068,9 +2068,12 @@ icl_dsc_compute_link_config(struct intel_dp *intel_dp,
>  			    int timeslots)
>  {
>  	int i, ret;
> +	int link_bpp;
> +
> +	link_bpp = intel_dp_output_bpp(pipe_config->output_format, pipe_bpp);

Here and in the xelpd version, using output_bpp instead of link_bpp or
just inlining intel_dp_output_bpp() at the single place it's used would
be better, but in any case the patch looks ok:

Reviewed-by: Imre Deak <imre.deak@intel.com>

>  
>  	/* Compressed BPP should be less than the Input DSC bpp */
> -	dsc_max_bpp = min(dsc_max_bpp, pipe_bpp - 1);
> +	dsc_max_bpp = min(dsc_max_bpp, link_bpp - 1);
>  
>  	for (i = 0; i < ARRAY_SIZE(valid_dsc_bpp); i++) {
>  		if (valid_dsc_bpp[i] < dsc_min_bpp)
> @@ -2113,6 +2116,7 @@ xelpd_dsc_compute_link_config(struct intel_dp *intel_dp,
>  	u8 bppx16_incr = drm_dp_dsc_sink_bpp_incr(connector->dp.dsc_dpcd);
>  	u16 compressed_bppx16;
>  	u8 bppx16_step;
> +	int link_bpp;
>  	int ret;
>  
>  	if (DISPLAY_VER(display) < 14 || bppx16_incr <= 1)
> @@ -2120,8 +2124,10 @@ xelpd_dsc_compute_link_config(struct intel_dp *intel_dp,
>  	else
>  		bppx16_step = 16 / bppx16_incr;
>  
> +	link_bpp = intel_dp_output_bpp(pipe_config->output_format, pipe_bpp);
> +
>  	/* Compressed BPP should be less than the Input DSC bpp */
> -	dsc_max_bpp = min(dsc_max_bpp << 4, (pipe_bpp << 4) - bppx16_step);
> +	dsc_max_bpp = min(dsc_max_bpp << 4, (link_bpp << 4) - bppx16_step);
>  	dsc_min_bpp = dsc_min_bpp << 4;
>  
>  	for (compressed_bppx16 = dsc_max_bpp;
> -- 
> 2.45.2
>