Re: [PATCH 02/14] drm/i915/dp: Add intel_dp_dsc_bpp_step_x16() helper to get DSC BPP precision

[Jani Nikula <jani.nikula@intel.com>]

On Fri, 31 Jan 2025, Imre Deak <imre.deak@intel.com> wrote:
> On Fri, Jan 31, 2025 at 02:49:55PM +0200, Jani Nikula wrote:
>> Add a platform independent helper for getting the supported DSC BPP step
>> for the link.
>> 
>> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
>> ---
>>  drivers/gpu/drm/i915/display/intel_dp.c | 21 ++++++++++++++++-----
>>  1 file changed, 16 insertions(+), 5 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
>> index ecf192262eb9..a7a5bb2075da 100644
>> --- a/drivers/gpu/drm/i915/display/intel_dp.c
>> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
>> @@ -2054,6 +2054,21 @@ static int dsc_src_max_compressed_bpp(struct intel_dp *intel_dp)
>>  		return 27;
>>  }
>>  
>> +/*
>> + * Note: for pre-13 display you still need to check the validity of each step.
>> + */
>> +static int intel_dp_dsc_bpp_step_x16(const struct intel_connector *connector)
>
> Nit: there was a guideline that these KMS objects should be passed around via
> non-const pointers vs. state pointers which should be const if possible.

At this point, xelpd_dsc_compute_link_config() only has the const
variable available. This changes later in the series.

>
>> +{
>> +	struct intel_display *display = to_intel_display(connector);
>> +	u8 incr = drm_dp_dsc_sink_bpp_incr(connector->dp.dsc_dpcd);
>> +
>> +	if (DISPLAY_VER(display) < 14 || !incr)
>> +		return fxp_q4_from_int(1);
>> +
>> +	/* fxp q4 */
>> +	return 16 / incr;
>
> Nit: could've been fxp_q4_from_int(1) / incr;

Good point, will fix.

>
> Regardless of the nits, patch looks ok:
>
> Reviewed-by: Imre Deak <imre.deak@intel.com>

Thanks!

>
>> +}
>> +
>>  /*
>>   * From a list of valid compressed bpps try different compressed bpp and find a
>>   * suitable link configuration that can support it.
>> @@ -2110,16 +2125,12 @@ xelpd_dsc_compute_link_config(struct intel_dp *intel_dp,
>>  			      int timeslots)
>>  {
>>  	struct intel_display *display = to_intel_display(intel_dp);
>> -	u8 bppx16_incr = drm_dp_dsc_sink_bpp_incr(connector->dp.dsc_dpcd);
>>  	int output_bpp = intel_dp_output_bpp(pipe_config->output_format, pipe_bpp);
>>  	u16 compressed_bppx16;
>>  	u8 bppx16_step;
>>  	int ret;
>>  
>> -	if (DISPLAY_VER(display) < 14 || bppx16_incr <= 1)
>> -		bppx16_step = 16;
>> -	else
>> -		bppx16_step = 16 / bppx16_incr;
>> +	bppx16_step = intel_dp_dsc_bpp_step_x16(connector);
>>  
>>  	/* Compressed BPP should be less than the Input DSC bpp */
>>  	dsc_max_bpp = min(dsc_max_bpp << 4, (output_bpp << 4) - bppx16_step);
>> -- 
>> 2.39.5
>> 

-- 
Jani Nikula, Intel