[Intel-gfx] [PATCH v2] drm/i915: intel_dp_link_is_valid() should only return status of link

[Pandiyan, Dhinakaran]

On Thu, 2016-08-11 at 15:23 -0700, Manasi Navare wrote:
> Intel_dp_link_is_valid() function reads the Link status registers
> and returns a boolean to indicate link is valid or not.
> If the link has lost lock and is not valid any more, link
> training is performed outside the function else previously trained link
> is retained.
> This gives us flexibility of checking whether link is valid and training
> it independently.
> 
> v2:
> * Changed the function name from intel_dp_check_link_status()
> to intel_dp_link_is_valid()  (Lukas Wunner)
> * Checks for CRTC and active CRTC are moved outside the
> intel_dp_link_is_valid() function (Rodrigo Vivi)
> 
> Signed-off-by: Manasi Navare <manasi.d.navare at intel.com>
> ---
>  drivers/gpu/drm/i915/intel_dp.c | 56 +++++++++++++++++++++++++++--------------
>  1 file changed, 37 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 364db90..891147d 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -3881,36 +3881,33 @@ go_again:
>  	return -EINVAL;
>  }
>  
> -static void
> -intel_dp_check_link_status(struct intel_dp *intel_dp)
> +static bool
> +intel_dp_link_is_valid(struct intel_dp *intel_dp)
>  {
> -	struct intel_encoder *intel_encoder = &dp_to_dig_port(intel_dp)->base;
>  	struct drm_device *dev = intel_dp_to_dev(intel_dp);
>  	u8 link_status[DP_LINK_STATUS_SIZE];
>  
>  	WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
>  
>  	if (!intel_dp_get_link_status(intel_dp, link_status)) {
> -		DRM_ERROR("Failed to get link status\n");
> -		return;
> +		DRM_DEBUG_KMS("Failed to get link status\n");
> +		return false;
>  	}
>  
> -	if (!intel_encoder->base.crtc)
> -		return;
> +	/* Check if the link is valid by reading the bits of Link status
> +	 * registers
> +	 */
> +	if (!drm_dp_channel_eq_ok(link_status, intel_dp->lane_count)) {
> +		DRM_DEBUG_KMS("Channel EQ or CR not ok, need to retrain\n");
drm_dp_channel_eq_ok() does not check for CR. Should we just say
"Channel EQ not ok" to preempt ambiguity while debugging ?

> +		return false;
> +	}
>  
> -	if (!to_intel_crtc(intel_encoder->base.crtc)->active)
> -		return;
> +	DRM_DEBUG_KMS("Link is good, no need to retrain\n");
The caller does not expect us to link train anymore, I don't think we
have to explicitly state "no need to retrain". Also, do we need debug
messages if the link is good?

> +	return true;
>  
> -	/* if link training is requested we should perform it always */
> -	if ((intel_dp->compliance_test_type == DP_TEST_LINK_TRAINING) ||
> -	    (!drm_dp_channel_eq_ok(link_status, intel_dp->lane_count))) {
> -		DRM_DEBUG_KMS("%s: channel EQ not ok, retraining\n",
> -			      intel_encoder->base.name);
> -		intel_dp_start_link_train(intel_dp);
> -		intel_dp_stop_link_train(intel_dp);
> -	}
>  }
>  
> +
>  /*
>   * According to DP spec
>   * 5.1.2:
> @@ -3928,6 +3925,8 @@ static bool
>  intel_dp_short_pulse(struct intel_dp *intel_dp)
>  {
>  	struct drm_device *dev = intel_dp_to_dev(intel_dp);
> +	struct intel_digital_port *intel_dig_port = dp_to_dig_port(intel_dp);
> +	struct intel_encoder *intel_encoder = &intel_dig_port->base;
>  	u8 sink_irq_vector = 0;
>  	u8 old_sink_count = intel_dp->sink_count;
>  	bool ret;
> @@ -3968,8 +3967,18 @@ intel_dp_short_pulse(struct intel_dp *intel_dp)
>  			DRM_DEBUG_DRIVER("CP or sink specific irq unhandled\n");
>  	}
>  
> +	/* Do not train the link if there is no crtc */
> +	if (!intel_encoder->base.crtc)
> +		return true;
> +	if (!to_intel_crtc(intel_encoder->base.crtc)->active)
> +		return true;
> +
I might be completely off base here. Shouldn't we keep the link valid
irrespective of whether there is an active crtc? I thought that is what
the refactoring is supposed to enable. Does intel_dp_short_pulse() get
called when there is a link loss during upfront link training? And in
that case, shouldn't we retrain even without a crtc? 

Besides that, how about using just one return?

struct drm_crtc *crtc = intel_encoder->base.crtc;

if (crtc == NULL || !to_intel_crtc(crtc)->active)
	return true;


>  	drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
> -	intel_dp_check_link_status(intel_dp);
> +	if (!intel_dp_link_is_valid(intel_dp) ||
> +	    intel_dp->compliance_test_type == DP_TEST_LINK_TRAINING) {
> +		intel_dp_start_link_train(intel_dp);
> +		intel_dp_stop_link_train(intel_dp);
> +	}
>  	drm_modeset_unlock(&dev->mode_config.connection_mutex);
>  
>  	return true;
> @@ -4298,8 +4307,17 @@ intel_dp_long_pulse(struct intel_connector *intel_connector)
>  		 * check links status, there has been known issues of
>  		 * link loss triggerring long pulse!!!!
>  		 */
> +		/* Do not train the link if there is no crtc */
> +		if (!intel_encoder->base.crtc)
> +			goto out;
> +		if (!to_intel_crtc(intel_encoder->base.crtc)->active)
> +			goto out;
> +
>  		drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
> -		intel_dp_check_link_status(intel_dp);
> +		if (!intel_dp_link_is_valid(intel_dp)) {
> +			intel_dp_start_link_train(intel_dp);
> +			intel_dp_stop_link_train(intel_dp);
> +		}
>  		drm_modeset_unlock(&dev->mode_config.connection_mutex);
>  		goto out;
>  	}