[PATCH 5/5] drm/i915/dp: Ignore max_requested_bpc if its too low for DSC

[Nautiyal, Ankit K]

On 9/26/2024 2:46 PM, Jani Nikula wrote:
> On Wed, 13 Dec 2023, Ankit Nautiyal <ankit.k.nautiyal at intel.com> wrote:
>> At the moment, while choosing the input bpc for DSC, we take into
>> account the max_requested_bpc property. This creates a problem, if the
>> max_requested_bpc is lower than the minimum bpc required by source with
>> DSC.
>>
>> So consider max_requested_bpc if its within the limits that we can
>> support with DSC.
>>
>> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal at intel.com>
>> ---
>>   drivers/gpu/drm/i915/display/intel_dp.c | 22 ++++++++++++++++++----
>>   1 file changed, 18 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
>> index e8aa2f469142..0014aa5ea652 100644
>> --- a/drivers/gpu/drm/i915/display/intel_dp.c
>> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
>> @@ -1638,6 +1638,16 @@ int intel_dp_dsc_max_src_input_bpc(struct drm_i915_private *i915)
>>   	return 12;
>>   }
>>   
>> +static int
>> +intel_dp_dsc_limit_max_bpc(int max_requested_bpc, int src_dsc_max_bpc, int src_dsc_min_bpc)
>> +{
>> +	/* Consider max_requested_bpc only if src can support it with DSC */
>> +	if (max_requested_bpc >= src_dsc_min_bpc)
>> +		return min(src_dsc_max_bpc, max_requested_bpc);
>> +
>> +	return src_dsc_max_bpc;
>> +}
>> +
>>   int intel_dp_dsc_compute_max_bpp(const struct intel_connector *connector,
>>   				 u8 max_req_bpc)
>>   {
>> @@ -1651,7 +1661,8 @@ int intel_dp_dsc_compute_max_bpp(const struct intel_connector *connector,
>>   	if (!dsc_max_bpc)
>>   		return dsc_max_bpc;
>>   
>> -	dsc_max_bpc = min(dsc_max_bpc, max_req_bpc);
>> +	dsc_max_bpc = intel_dp_dsc_limit_max_bpc(max_req_bpc, dsc_max_bpc,
>> +						 intel_dp_dsc_min_src_input_bpc(i915));
> Somehow that doesn't read so well.
>
> I think something like this would improve clarity:
>
> 	dsc_min_bpc = intel_dp_dsc_min_src_input_bpc(i915);
> 	dsc_max_bpc = intel_dp_dsc_max_src_input_bpc(i915);
>
> 	max_req_bpc = clamp(max_req_bpc, dsc_min_bpc, dsc_max_bpc);
>
> i.e. clamp the request to reasonable limits. That's more like regular
> input checking. That should be done *everywhere* when
> conn_state->max_requested_bpc is used.
>
> Then min(dsc_max_bpc, max_req_bpc) is no longer needed because
> max_req_bpc <= dsc_max_bpc is guaranteed.
>
> IOW this becomes:
>
> 	dsc_max_bpc = clamp(max_req_bpc, dsc_min_bpc, dsc_max_bpc);

You are right, clamping is the correct thing here.

Also realized that we actually do not need to explicitly check 
max_req_bpc, as its already taken into account.

I have sent new rev of the series with the above addressed and some more 
refactoring.

Regards,

Ankit


>
> BR,
> Jani.
>
>>   
>>   	num_bpc = drm_dp_dsc_sink_supported_input_bpcs(connector->dp.dsc_dpcd,
>>   						       dsc_bpc);
>> @@ -2039,8 +2050,11 @@ bool is_dsc_pipe_bpp_sufficient(struct drm_i915_private *i915,
>>   {
>>   	int dsc_max_bpc, dsc_min_bpc, dsc_max_pipe_bpp, dsc_min_pipe_bpp;
>>   
>> -	dsc_max_bpc = min(intel_dp_dsc_max_src_input_bpc(i915), conn_state->max_requested_bpc);
>>   	dsc_min_bpc = intel_dp_dsc_min_src_input_bpc(i915);
>> +	dsc_max_bpc = intel_dp_dsc_max_src_input_bpc(i915);
>> +
>> +	dsc_max_bpc = intel_dp_dsc_limit_max_bpc(conn_state->max_requested_bpc,
>> +						 dsc_max_bpc, dsc_min_bpc);
>>   
>>   	dsc_max_pipe_bpp = min(dsc_max_bpc * 3, limits->pipe.max_bpp);
>>   	dsc_min_pipe_bpp = max(dsc_min_bpc * 3, limits->pipe.min_bpp);
>> @@ -2100,14 +2114,14 @@ static int intel_dp_dsc_compute_pipe_bpp(struct intel_dp *intel_dp,
>>   		}
>>   	}
>>   
>> +	dsc_min_bpc = intel_dp_dsc_min_src_input_bpc(i915);
>>   	dsc_max_bpc = intel_dp_dsc_max_src_input_bpc(i915);
>>   	if (!dsc_max_bpc)
>>   		return -EINVAL;
>>   
>> -	dsc_max_bpc = min(dsc_max_bpc, max_req_bpc);
>> +	dsc_max_bpc = intel_dp_dsc_limit_max_bpc(max_req_bpc, dsc_max_bpc, dsc_min_bpc);
>>   	dsc_max_bpp = min(dsc_max_bpc * 3, limits->pipe.max_bpp);
>>   
>> -	dsc_min_bpc = intel_dp_dsc_min_src_input_bpc(i915);
>>   	dsc_min_bpp = max(dsc_min_bpc * 3, limits->pipe.min_bpp);
>>   
>>   	/*