Re: [Intel-gfx] [PATCH 2/2] drm/i915/dsc: clarify DSC support for pipe A on ICL

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

On Wed, 11 Dec 2019, Manasi Navare <manasi.d.navare@intel.com> wrote:
> On Wed, Dec 11, 2019 at 06:23:47PM +0200, Jani Nikula wrote:
>> The check for cpu_transcoder != TRANSCODER_A is more magic than
>> necessary, and potentially misleading. Before TGL, DSC is supported on
>> pipe A if, and only if, it's used with eDP or DSI transcoders. No
>> functional changes.
>>
>
> Hmm, so we could still use PIPE_A but if its eDP or DSI it would use
> TRANSCODER_EDP or TRANSCODER_DSI and that should still work?

Correct, because on gen 11 eDP/DSI have a DSC engine in front of the
transcoder.

> So its simpler to say that if it is PIPE_A && transcoder_A then it doesnt
> support DSC?
> Wouldnt it be simpler to change the condition to :
> if (INTEL_GEN(i915) >= 10 && !(pipe_A && transcode_A)
>      return true;

The simplest is really the code as it is... but it's not clear, and
would deserve a comment. But I very much prefer self-documenting code
over comments explaining surprising code. So I'd like to spell out the
eDP/DSI transcoders here.

BR,
Jani.

>
> Regards
> Manasi
>  
>> Cc: Manasi Navare <manasi.d.navare@intel.com>
>> Cc: Vandita Kulkarni <vandita.kulkarni@intel.com>
>> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
>> ---
>>  drivers/gpu/drm/i915/display/intel_vdsc.c | 8 +++++++-
>>  1 file changed, 7 insertions(+), 1 deletion(-)
>> 
>> diff --git a/drivers/gpu/drm/i915/display/intel_vdsc.c b/drivers/gpu/drm/i915/display/intel_vdsc.c
>> index e6f60be9ee84..41718f721484 100644
>> --- a/drivers/gpu/drm/i915/display/intel_vdsc.c
>> +++ b/drivers/gpu/drm/i915/display/intel_vdsc.c
>> @@ -337,7 +337,10 @@ static const struct rc_parameters *get_rc_params(u16 compressed_bpp,
>>  bool intel_dsc_source_support(struct intel_encoder *encoder,
>>  			      const struct intel_crtc_state *crtc_state)
>>  {
>> +	const struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
>>  	struct drm_i915_private *i915 = to_i915(encoder->base.dev);
>> +	enum transcoder cpu_transcoder = crtc_state->cpu_transcoder;
>> +	enum pipe pipe = crtc->pipe;
>>  
>>  	if (!INTEL_INFO(i915)->display.has_dsc)
>>  		return false;
>> @@ -347,7 +350,10 @@ bool intel_dsc_source_support(struct intel_encoder *encoder,
>>  		return true;
>>  
>>  	if (INTEL_GEN(i915) >= 10 &&
>> -	    crtc_state->cpu_transcoder != TRANSCODER_A)
>> +	    (pipe != PIPE_A ||
>> +	     (cpu_transcoder == TRANSCODER_EDP ||
>> +	      cpu_transcoder == TRANSCODER_DSI_0 ||
>> +	      cpu_transcoder == TRANSCODER_DSI_1)))
>>  		return true;
>>  
>>  	return false;
>> -- 
>> 2.20.1
>> 

-- 
Jani Nikula, Intel Open Source Graphics Center
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