Re: [PATCH 02/15] drm/i915: Don't pass *DP around to link training functions

[Ander Conselvan De Oliveira <conselvan2@gmail.com>]

On Mon, 2015-10-19 at 10:15 +0530, Thulasimani, Sivakumar wrote:
> 
> On 10/5/2015 12:31 PM, Ander Conselvan de Oliveira wrote:
> > It just makes the code more confusing, so just reference intel_dp_>DP
> > directly. The old behavior of not updating the value in intel_dp if link
> > training fail is preserved by saving the previous value of DP in the
> > stack and restoring the old value in case of failure.
> > 
> > Signed-off-by: Ander Conselvan de Oliveira <
> > ander.conselvan.de.oliveira@intel.com>
> > --
> > 
> > I'm not sure the old behavior is correct, but to err in the side of
> > caution I tried not to change it.
> > 
> > ---
> >   drivers/gpu/drm/i915/intel_dp.c | 66 ++++++++++++++++++++-----------------
> > ----
> >   1 file changed, 33 insertions(+), 33 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_dp.c
> > b/drivers/gpu/drm/i915/intel_dp.c
> > index c420edf..391a367 100644
> > --- a/drivers/gpu/drm/i915/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > @@ -3601,7 +3601,6 @@ intel_dp_set_signal_levels(struct intel_dp *intel_dp,
> > uint32_t *DP)
> >   
> >   static bool
> >   intel_dp_set_link_train(struct intel_dp *intel_dp,
> > -			uint32_t *DP,
> >   			uint8_t dp_train_pat)
> >   {
> >   	struct intel_digital_port *intel_dig_port =
> > dp_to_dig_port(intel_dp);
> > @@ -3610,9 +3609,9 @@ intel_dp_set_link_train(struct intel_dp *intel_dp,
> >   	uint8_t buf[sizeof(intel_dp->train_set) + 1];
> >   	int ret, len;
> >   
> > -	_intel_dp_set_link_train(intel_dp, DP, dp_train_pat);
> > +	_intel_dp_set_link_train(intel_dp, &intel_dp->DP, dp_train_pat);
> >   
> > -	I915_WRITE(intel_dp->output_reg, *DP);
> > +	I915_WRITE(intel_dp->output_reg, intel_dp->DP);
> >   	POSTING_READ(intel_dp->output_reg);
> >   
> >   	buf[0] = dp_train_pat;
> > @@ -3633,17 +3632,17 @@ intel_dp_set_link_train(struct intel_dp *intel_dp,
> >   }
> >   
> >   static bool
> > -intel_dp_reset_link_train(struct intel_dp *intel_dp, uint32_t *DP,
> > +intel_dp_reset_link_train(struct intel_dp *intel_dp,
> >   			uint8_t dp_train_pat)
> >   {
> >   	if (!intel_dp->train_set_valid)
> >   		memset(intel_dp->train_set, 0, sizeof(intel_dp
> > ->train_set));
> > -	intel_dp_set_signal_levels(intel_dp, DP);
> > -	return intel_dp_set_link_train(intel_dp, DP, dp_train_pat);
> > +	intel_dp_set_signal_levels(intel_dp, &intel_dp->DP);
> > +	return intel_dp_set_link_train(intel_dp, dp_train_pat);
> >   }
> >   
> >   static bool
> > -intel_dp_update_link_train(struct intel_dp *intel_dp, uint32_t *DP,
> > +intel_dp_update_link_train(struct intel_dp *intel_dp,
> >   			   const uint8_t link_status[DP_LINK_STATUS_SIZE])
> >   {
> >   	struct intel_digital_port *intel_dig_port =
> > dp_to_dig_port(intel_dp);
> > @@ -3652,9 +3651,9 @@ intel_dp_update_link_train(struct intel_dp *intel_dp,
> > uint32_t *DP,
> >   	int ret;
> >   
> >   	intel_get_adjust_train(intel_dp, link_status);
> > -	intel_dp_set_signal_levels(intel_dp, DP);
> > +	intel_dp_set_signal_levels(intel_dp, &intel_dp->DP);
> >   
> > -	I915_WRITE(intel_dp->output_reg, *DP);
> > +	I915_WRITE(intel_dp->output_reg, intel_dp->DP);
> >   	POSTING_READ(intel_dp->output_reg);
> >   
> >   	ret = drm_dp_dpcd_write(&intel_dp->aux, DP_TRAINING_LANE0_SET,
> > @@ -3695,7 +3694,7 @@ static void intel_dp_set_idle_link_train(struct
> > intel_dp *intel_dp)
> >   }
> >   
> >   /* Enable corresponding port and start training pattern 1 */
> > -static void
> > +static bool
> >   intel_dp_link_training_clock_recovery(struct intel_dp *intel_dp)
> >   {
> >   	struct drm_encoder *encoder = &dp_to_dig_port(intel_dp)
> > ->base.base;
> > @@ -3703,9 +3702,9 @@ intel_dp_link_training_clock_recovery(struct intel_dp
> > *intel_dp)
> >   	int i;
> >   	uint8_t voltage;
> >   	int voltage_tries, loop_tries;
> > -	uint32_t DP = intel_dp->DP;
> >   	uint8_t link_config[2];
> >   	uint8_t link_bw, rate_select;
> > +	uint8_t link_status[DP_LINK_STATUS_SIZE];
> >   
> >   	if (HAS_DDI(dev))
> >   		intel_ddi_prepare_link_retrain(encoder);
> > @@ -3727,22 +3726,20 @@ intel_dp_link_training_clock_recovery(struct
> > intel_dp *intel_dp)
> >   	link_config[1] = DP_SET_ANSI_8B10B;
> >   	drm_dp_dpcd_write(&intel_dp->aux, DP_DOWNSPREAD_CTRL, link_config,
> > 2);
> >   
> > -	DP |= DP_PORT_EN;
> > +	intel_dp->DP |= DP_PORT_EN;
> >   
> >   	/* clock recovery */
> > -	if (!intel_dp_reset_link_train(intel_dp, &DP,
> > +	if (!intel_dp_reset_link_train(intel_dp,
> >   				       DP_TRAINING_PATTERN_1 |
> >   				       DP_LINK_SCRAMBLING_DISABLE)) {
> >   		DRM_ERROR("failed to enable link training\n");
> > -		return;
> > +		return false;
> >   	}
> >   
> >   	voltage = 0xff;
> >   	voltage_tries = 0;
> >   	loop_tries = 0;
> >   	for (;;) {
> > -		uint8_t link_status[DP_LINK_STATUS_SIZE];
> > -
> >   		drm_dp_link_train_clock_recovery_delay(intel_dp->dpcd);
> >   		if (!intel_dp_get_link_status(intel_dp, link_status)) {
> >   			DRM_ERROR("failed to get link status\n");
> > @@ -3762,11 +3759,11 @@ intel_dp_link_training_clock_recovery(struct
> > intel_dp *intel_dp)
> >   			DRM_DEBUG_KMS("clock recovery not ok, reset");
> >   			/* clear the flag as we are not reusing train set
> > */
> >   			intel_dp->train_set_valid = false;
> > -			if (!intel_dp_reset_link_train(intel_dp, &DP,
> > +			if (!intel_dp_reset_link_train(intel_dp,
> >   						      
> >  DP_TRAINING_PATTERN_1 |
> >   						      
> >  DP_LINK_SCRAMBLING_DISABLE)) {
> >   				DRM_ERROR("failed to enable link
> > training\n");
> > -				return;
> > +				return false;
> >   			}
> >   			continue;
> >   		}
> > @@ -3781,7 +3778,7 @@ intel_dp_link_training_clock_recovery(struct intel_dp
> > *intel_dp)
> >   				DRM_ERROR("too many full retries, give
> > up\n");
> >   				break;
> >   			}
> > -			intel_dp_reset_link_train(intel_dp, &DP,
> > +			intel_dp_reset_link_train(intel_dp,
> >   						  DP_TRAINING_PATTERN_1 |
> >   						 
> >  DP_LINK_SCRAMBLING_DISABLE);
> >   			voltage_tries = 0;
> > @@ -3800,23 +3797,22 @@ intel_dp_link_training_clock_recovery(struct
> > intel_dp *intel_dp)
> >   		voltage = intel_dp->train_set[0] &
> > DP_TRAIN_VOLTAGE_SWING_MASK;
> >   
> >   		/* Update training set as requested by target */
> > -		if (!intel_dp_update_link_train(intel_dp, &DP,
> > link_status)) {
> > +		if (!intel_dp_update_link_train(intel_dp, link_status)) {
> >   			DRM_ERROR("failed to update link training\n");
> >   			break;
> >   		}
> >   	}
> >   
> > -	intel_dp->DP = DP;
> > +	return drm_dp_clock_recovery_ok(link_status, intel_dp->lane_count);
> why are we calling the same function again? in best case this function 
> is called and returned true,
>   or worst case it was never called. so it will be simpler if we store 
> the return value of this function
> inside the loop and return that here ?

I missed this comment earlier. I don't think calling drm_dp_clock_recovery_ok()
would have a big impact, since it is a very simple function. But I can add a
variable if that is preferred.

Ander


> >   }
> >   
> > -static void
> > +static bool
> >   intel_dp_link_training_channel_equalization(struct intel_dp *intel_dp)
> >   {
> >   	struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
> >   	struct drm_device *dev = dig_port->base.base.dev;
> >   	bool channel_eq = false;
> >   	int tries, cr_tries;
> > -	uint32_t DP = intel_dp->DP;
> >   	uint32_t training_pattern = DP_TRAINING_PATTERN_2;
> >   
> >   	/*
> > @@ -3835,11 +3831,11 @@ intel_dp_link_training_channel_equalization(struct
> > intel_dp *intel_dp)
> >   		DRM_ERROR("5.4 Gbps link rate without HBR2/TPS3
> > support\n");
> >   
> >   	/* channel equalization */
> > -	if (!intel_dp_set_link_train(intel_dp, &DP,
> > +	if (!intel_dp_set_link_train(intel_dp,
> >   				     training_pattern |
> >   				     DP_LINK_SCRAMBLING_DISABLE)) {
> >   		DRM_ERROR("failed to start channel equalization\n");
> > -		return;
> > +		return false;
> >   	}
> >   
> >   	tries = 0;
> > @@ -3864,7 +3860,7 @@ intel_dp_link_training_channel_equalization(struct
> > intel_dp *intel_dp)
> >   					      intel_dp->lane_count)) {
> >   			intel_dp->train_set_valid = false;
> >   			intel_dp_link_training_clock_recovery(intel_dp);
> > -			intel_dp_set_link_train(intel_dp, &DP,
> > +			intel_dp_set_link_train(intel_dp,
> >   						training_pattern |
> >   						DP_LINK_SCRAMBLING_DISABLE
> > );
> >   			cr_tries++;
> > @@ -3881,7 +3877,7 @@ intel_dp_link_training_channel_equalization(struct
> > intel_dp *intel_dp)
> >   		if (tries > 5) {
> >   			intel_dp->train_set_valid = false;
> >   			intel_dp_link_training_clock_recovery(intel_dp);
> > -			intel_dp_set_link_train(intel_dp, &DP,
> > +			intel_dp_set_link_train(intel_dp,
> >   						training_pattern |
> >   						DP_LINK_SCRAMBLING_DISABLE
> > );
> >   			tries = 0;
> > @@ -3890,7 +3886,7 @@ intel_dp_link_training_channel_equalization(struct
> > intel_dp *intel_dp)
> >   		}
> >   
> >   		/* Update training set as requested by target */
> > -		if (!intel_dp_update_link_train(intel_dp, &DP,
> > link_status)) {
> > +		if (!intel_dp_update_link_train(intel_dp, link_status)) {
> >   			DRM_ERROR("failed to update link training\n");
> >   			break;
> >   		}
> > @@ -3899,25 +3895,29 @@ intel_dp_link_training_channel_equalization(struct
> > intel_dp *intel_dp)
> >   
> >   	intel_dp_set_idle_link_train(intel_dp);
> >   
> > -	intel_dp->DP = DP;
> > -
> >   	if (channel_eq) {
> >   		intel_dp->train_set_valid = true;
> >   		DRM_DEBUG_KMS("Channel EQ done. DP Training
> > successful\n");
> > +		return true;
> > +	} else {
> > +		return false;
> >   	}
> >   }
> >   
> >   void intel_dp_stop_link_train(struct intel_dp *intel_dp)
> >   {
> > -	intel_dp_set_link_train(intel_dp, &intel_dp->DP,
> > +	intel_dp_set_link_train(intel_dp,
> >   				DP_TRAINING_PATTERN_DISABLE);
> >   }
> >   
> >   void
> >   intel_dp_start_link_train(struct intel_dp *intel_dp)
> >   {
> > -	intel_dp_link_training_clock_recovery(intel_dp);
> > -	intel_dp_link_training_channel_equalization(intel_dp);
> > +	uint32_t DP = intel_dp->DP;
> > +
> > +	if (!intel_dp_link_training_clock_recovery(intel_dp) ||
> > +	    !intel_dp_link_training_channel_equalization(intel_dp))
> > +		intel_dp->DP = DP;
> it is wrong to restore the value of DP here, we have modified the value 
> of port/ddi already inside the two functions.
> if either of these two steps fail we should call stop link training and 
> follow it with bspec disable sequence.
> so saving and restoring will not help us in anyway but more hide the 
> real status of HW.
> >   }
> >   
> >   static void
> 
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