[Intel-gfx] [PATCH 2/3] drm/i915: Wait for pending modesets to complete before trying link training

[Maarten Lankhorst]

Op 26-01-17 om 19:31 schreef Ville Syrjälä:
> On Mon, Jan 09, 2017 at 06:06:57PM +0100, Maarten Lankhorst wrote:
>> We're protected by the connection_mutex lock against blocking modesets,
>> but nonblocking modesets are performed without any locking. This is
>> causing WARN in drm_wait_for_vblank and in general it's better to wait
>> before modeset completes before trying anything.
>>
>> Signed-off-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
>> ---
>>  drivers/gpu/drm/i915/intel_dp.c | 51 +++++++++++++++++++++++++++++++----------
>>  1 file changed, 39 insertions(+), 12 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
>> index fb12896bafee..71882d887393 100644
>> --- a/drivers/gpu/drm/i915/intel_dp.c
>> +++ b/drivers/gpu/drm/i915/intel_dp.c
>> @@ -4080,24 +4080,38 @@ intel_dp_check_link_status(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];
>> +	struct drm_modeset_acquire_ctx ctx;
>> +	struct intel_connector *intel_connector = intel_dp->attached_connector;
>> +	int ret;
>> +	struct drm_crtc *crtc;
>>  
>> -	WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
>> +	drm_modeset_acquire_init(&ctx, 0);
>> +
>> +retry:
>> +	ret = drm_modeset_lock(&dev->mode_config.connection_mutex, &ctx);
>> +	if (ret)
>> +		goto out;
>>  
>>  	if (!intel_dp_get_link_status(intel_dp, link_status)) {
>>  		DRM_ERROR("Failed to get link status\n");
>> -		return;
>> +		goto out;
>>  	}
>>  
>> -	if (!intel_encoder->base.crtc)
>> -		return;
>> +	crtc = intel_connector->base.state->crtc;
>> +	if (!crtc)
>> +		goto out;
>>  
>> -	if (!to_intel_crtc(intel_encoder->base.crtc)->active)
>> -		return;
>> +	ret = drm_modeset_lock(&crtc->mutex, &ctx);
>> +	if (ret)
>> +		goto out;
>> +
>> +	if (!crtc->state->active)
>> +		goto out;
>>  
>>  	/* FIXME: we need to synchronize this sort of stuff with hardware
>>  	 * readout. Currently fast link training doesn't work on boot-up. */
>>  	if (!intel_dp->lane_count)
>> -		return;
>> +		goto out;
>>  
>>  	/* if link training is requested we should perform it always */
>>  	if ((intel_dp->compliance.test_type == DP_TEST_LINK_TRAINING) ||
>> @@ -4105,8 +4119,26 @@ intel_dp_check_link_status(struct intel_dp *intel_dp)
>>  		DRM_DEBUG_KMS("%s: channel EQ not ok, retraining\n",
>>  			      intel_encoder->base.name);
>>  
>> +		if (drm_atomic_crtc_needs_modeset(crtc->state)) {
>> +			/* wait for atomic modeset to complete */
>> +			ret = drm_atomic_helper_wait_for_hw_done(crtc);
>> +			if (ret < 0)
>> +				DRM_ERROR("Waiting for hw_done timed out\n");
> I wonder if we should just skip the hw frobbing in this case. I guess it
> might still restore the link if the commit just somehow got stuck
> somewhere non-critical.
Hm,  we could check if the link training is still required after the wait.
Maybe even do the wait unlocked, since it might take an arbitrary amount of time
and then retry?
>> +		}
>> +
>>  		intel_dp_retrain_link(intel_dp);
>>  	}
>> +
>> +out:
>> +	if (ret == -EDEADLK) {
>> +		drm_modeset_backoff(&ctx);
>> +		goto retry;
>> +	}
>> +
>> +	drm_modeset_drop_locks(&ctx);
>> +	drm_modeset_acquire_fini(&ctx);
>> +	if (ret)
>> +		DRM_ERROR("Locking failed with %i\n", ret);
> This seems incorrect if we timed out on the wait. Maybe just
> clear ret after the hw_done wait?
>
>>  }
>>  
>>  /*
>> @@ -4125,7 +4157,6 @@ intel_dp_check_link_status(struct intel_dp *intel_dp)
>>  static bool
>>  intel_dp_short_pulse(struct intel_dp *intel_dp)
>>  {
>> -	struct drm_device *dev = intel_dp_to_dev(intel_dp);
>>  	u8 sink_irq_vector = 0;
>>  	u8 old_sink_count = intel_dp->sink_count;
>>  	bool ret;
>> @@ -4164,9 +4195,7 @@ intel_dp_short_pulse(struct intel_dp *intel_dp)
>>  			DRM_DEBUG_DRIVER("CP or sink specific irq unhandled\n");
>>  	}
>>  
>> -	drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
>>  	intel_dp_check_link_status(intel_dp);
>> -	drm_modeset_unlock(&dev->mode_config.connection_mutex);
>>  
>>  	return true;
>>  }
>> @@ -4499,9 +4528,7 @@ intel_dp_long_pulse(struct intel_connector *intel_connector)
>>  		 * check links status, there has been known issues of
>>  		 * link loss triggerring long pulse!!!!
>>  		 */
>> -		drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
>>  		intel_dp_check_link_status(intel_dp);
>> -		drm_modeset_unlock(&dev->mode_config.connection_mutex);
>>  		goto out;
>>  	}
>>  
>> -- 
>> 2.7.4
>>
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