Re: [Intel-gfx] [PATCH v4 1/2] drm/i915/dp: abstract intel_dp_lane_max_vswing_reached()

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

On Thu, 07 Oct 2021, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> On Thu, Oct 07, 2021 at 04:39:07PM +0300, Jani Nikula wrote:
>> Add per-lane abstraction for max vswing reached to make follow-up
>> cleaner, as this one reverses the conditions.
>> 
>> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
>> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
>> ---
>>  .../drm/i915/display/intel_dp_link_training.c | 42 +++++++++++--------
>>  1 file changed, 25 insertions(+), 17 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/i915/display/intel_dp_link_training.c b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
>> index 1a943ae38a6b..d239d72bfcf2 100644
>> --- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
>> +++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
>> @@ -515,29 +515,37 @@ intel_dp_update_link_train(struct intel_dp *intel_dp,
>>  	return ret == crtc_state->lane_count;
>>  }
>>  
>> +/*
>> + * FIXME: The DP spec is very confusing here, also the Link CTS spec seems to
>> + * have self contradicting tests around this area.
>> + *
>> + * In lieu of better ideas let's just stop when we've reached the max supported
>> + * vswing with its max pre-emphasis, which is either 2+1 or 3+0 depending on
>> + * whether vswing level 3 is supported or not.
>> + */
>> +static bool intel_dp_lane_max_vswing_reached(u8 train_set_lane)
>> +{
>> +	u8 v = (train_set_lane & DP_TRAIN_VOLTAGE_SWING_MASK) >>
>> +		DP_TRAIN_VOLTAGE_SWING_SHIFT;
>> +	u8 p = (train_set_lane & DP_TRAIN_PRE_EMPHASIS_MASK) >>
>> +		DP_TRAIN_PRE_EMPHASIS_SHIFT;
>> +
>> +	if (train_set_lane & DP_TRAIN_MAX_SWING_REACHED)
>> +		return true;
>> +
>> +	if (v + p == 3)
>> +		return true;
>
> We want both to be true at the same time.

D'oh! See, that's why I split it up from the other patch, but fumbled it
anyway.

Thanks.

BR,
Jani.

>
>> +
>> +	return false;
>> +}
>> +
>>  static bool intel_dp_link_max_vswing_reached(struct intel_dp *intel_dp,
>>  					     const struct intel_crtc_state *crtc_state)
>>  {
>>  	int lane;
>>  
>> -	/*
>> -	 * FIXME: The DP spec is very confusing here, also the Link CTS
>> -	 * spec seems to have self contradicting tests around this area.
>> -	 *
>> -	 * In lieu of better ideas let's just stop when we've reached the
>> -	 * max supported vswing with its max pre-emphasis, which is either
>> -	 * 2+1 or 3+0 depending on whether vswing level 3 is supported or not.
>> -	 */
>>  	for (lane = 0; lane < crtc_state->lane_count; lane++) {
>> -		u8 v = (intel_dp->train_set[lane] & DP_TRAIN_VOLTAGE_SWING_MASK) >>
>> -			DP_TRAIN_VOLTAGE_SWING_SHIFT;
>> -		u8 p = (intel_dp->train_set[lane] & DP_TRAIN_PRE_EMPHASIS_MASK) >>
>> -			DP_TRAIN_PRE_EMPHASIS_SHIFT;
>> -
>> -		if ((intel_dp->train_set[lane] & DP_TRAIN_MAX_SWING_REACHED) == 0)
>> -			return false;
>> -
>> -		if (v + p != 3)
>> +		if (!intel_dp_lane_max_vswing_reached(intel_dp->train_set[lane]))
>>  			return false;
>>  	}
>>  
>> -- 
>> 2.30.2

-- 
Jani Nikula, Intel Open Source Graphics Center