[PATCH 01/14] drm/i915/dp: Iterate DSC BPP from high to low on all platforms

[Imre Deak]

On Fri, Jan 31, 2025 at 02:49:54PM +0200, Jani Nikula wrote:
> Commit 1c56e9a39833 ("drm/i915/dp: Get optimal link config to have best
> compressed bpp") tries to find the best compressed bpp for the
> link. However, it iterates from max to min bpp on display 13+, and from
> min to max on other platforms. This presumably leads to minimum
> compressed bpp always being chosen on display 11-12.
> 
> Iterate from high to low on all platforms to actually use the best
> possible compressed bpp.
> 
> Fixes: 1c56e9a39833 ("drm/i915/dp: Get optimal link config to have best compressed bpp")
> Cc: Ankit Nautiyal <ankit.k.nautiyal at intel.com>
> Cc: Imre Deak <imre.deak at intel.com>
> Cc: <stable at vger.kernel.org> # v6.7+
> Signed-off-by: Jani Nikula <jani.nikula at intel.com>

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

> ---
>  drivers/gpu/drm/i915/display/intel_dp.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index d1b4fd542a1f..ecf192262eb9 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -2073,11 +2073,10 @@ icl_dsc_compute_link_config(struct intel_dp *intel_dp,
>  	/* Compressed BPP should be less than the Input DSC bpp */
>  	dsc_max_bpp = min(dsc_max_bpp, output_bpp - 1);
>  
> -	for (i = 0; i < ARRAY_SIZE(valid_dsc_bpp); i++) {
> -		if (valid_dsc_bpp[i] < dsc_min_bpp)
> +	for (i = ARRAY_SIZE(valid_dsc_bpp) - 1; i >= 0; i--) {
> +		if (valid_dsc_bpp[i] < dsc_min_bpp ||
> +		    valid_dsc_bpp[i] > dsc_max_bpp)
>  			continue;
> -		if (valid_dsc_bpp[i] > dsc_max_bpp)
> -			break;
>  
>  		ret = dsc_compute_link_config(intel_dp,
>  					      pipe_config,
> -- 
> 2.39.5
>