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

[Nautiyal, Ankit K]

On 1/31/2025 6:19 PM, 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>

Thanks for the fix. I think I intended to iterate from max to min in 
initial version of the patch (atleast the one sent to trybot [1]), but 
some how messed it up while rebasing.

Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal at intel.com>

[1] 
https://lists.freedesktop.org/archives/intel-gfx-trybot/2022-June/129432.html

> ---
>   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,