Re: [PATCH v2 19/21] drm/i915/dp: Add debugfs entry to force link training failure

[Imre Deak <imre.deak@intel.com>]

On Thu, May 23, 2024 at 06:29:34PM +0300, Ville Syrjälä wrote:
> On Mon, May 20, 2024 at 09:58:17PM +0300, Imre Deak wrote:
> > Add a connector debugfs entry to force a failure during the following
> > 1-2 link training. The entry will auto-reset after the specified link
> > training events are complete.
> > 
> > v2: Add the entry from intel_dp_link_training.c (Jani)
> > 
> > Cc: Jani Nikula <jani.nikula@intel.com>
> > Signed-off-by: Imre Deak <imre.deak@intel.com>
> > ---
> >  .../drm/i915/display/intel_display_types.h    |  1 +
> >  .../drm/i915/display/intel_dp_link_training.c | 52 ++++++++++++++++++-
> >  2 files changed, 52 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
> > index e1c41cece249d..dbe1468fe471d 100644
> > --- a/drivers/gpu/drm/i915/display/intel_display_types.h
> > +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
> > @@ -1770,6 +1770,7 @@ struct intel_dp {
> >  		bool retrain_disabled;
> >  		/* Sequential link training failures after a passing LT */
> >  		int seq_train_failures;
> > +		int force_train_failure;
> >  	} link;
> >  	bool reset_link_params;
> >  	int mso_link_count;
> > 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 764187bc42ff9..b40148a42f442 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> > @@ -1489,7 +1489,10 @@ void intel_dp_start_link_train(struct intel_atomic_state *state,
> >  	else
> >  		passed = intel_dp_link_train_all_phys(intel_dp, crtc_state, lttpr_count);
> >  
> > -	if (passed) {
> > +	if (intel_dp->link.force_train_failure) {
> > +		intel_dp->link.force_train_failure--;
> > +		lt_dbg(intel_dp, DP_PHY_DPRX, "Forcing link training failure\n");
> > +	} else if (passed) {
> >  		intel_dp->link.seq_train_failures = 0;
> >  		intel_ddi_queue_link_check(dig_port, 2000);
> >  		return;
> > @@ -1799,6 +1802,50 @@ static int i915_dp_max_lane_count_show(void *data, u64 *val)
> >  }
> >  DEFINE_DEBUGFS_ATTRIBUTE(i915_dp_max_lane_count_fops, i915_dp_max_lane_count_show, NULL, "%llu\n");
> >  
> > +static int i915_dp_force_link_training_failure_show(void *data, u64 *val)
> > +{
> > +	struct intel_connector *connector = to_intel_connector(data);
> > +	struct drm_i915_private *i915 = to_i915(connector->base.dev);
> > +	struct intel_dp *intel_dp;
> > +	int err;
> > +
> > +	err = drm_modeset_lock_single_interruptible(&i915->drm.mode_config.connection_mutex);
> > +	if (err)
> > +		return err;
> > +
> > +	intel_dp = intel_connector_to_intel_dp(connector);
> > +	*val = intel_dp->link.force_train_failure;
> > +
> > +	drm_modeset_unlock(&i915->drm.mode_config.connection_mutex);
> > +
> > +	return 0;
> > +}
> > +
> > +static int i915_dp_force_link_training_failure_write(void *data, u64 val)
> > +{
> > +	struct intel_connector *connector = to_intel_connector(data);
> > +	struct drm_i915_private *i915 = to_i915(connector->base.dev);
> > +	struct intel_dp *intel_dp;
> > +	int err;
> > +
> > +	if (val > 2)
> 
> Why 2 specifically?

There are 2 back-to-back link trainings that can fail after a modeset or
later after detecting a bad link state, the initial one and a second
with the same LT parameters. That's followed by reducing the LT
parameters and probably a modeset changing the mode.

> > +		return -EINVAL;
> > +
> > +	err = drm_modeset_lock_single_interruptible(&i915->drm.mode_config.connection_mutex);
> > +	if (err)
> > +		return err;
> > +
> > +	intel_dp = intel_connector_to_intel_dp(connector);
> > +	intel_dp->link.force_train_failure = val;
> > +
> > +	drm_modeset_unlock(&i915->drm.mode_config.connection_mutex);
> > +
> > +	return 0;
> > +}
> > +DEFINE_DEBUGFS_ATTRIBUTE(i915_dp_force_link_training_failure_fops,
> > +			 i915_dp_force_link_training_failure_show,
> > +			 i915_dp_force_link_training_failure_write, "%llu\n");
> > +
> >  void intel_dp_link_training_debugfs_add(struct intel_connector *connector)
> >  {
> >  	struct dentry *root = connector->base.debugfs_entry;
> > @@ -1818,4 +1865,7 @@ void intel_dp_link_training_debugfs_add(struct intel_connector *connector)
> >  
> >  	debugfs_create_file("i915_dp_max_lane_count", 0444, root,
> >  			    connector, &i915_dp_max_lane_count_fops);
> > +
> > +	debugfs_create_file("i915_dp_force_link_training_failure", 0644, root,
> > +			    connector, &i915_dp_force_link_training_failure_fops);
> >  }
> > -- 
> > 2.43.3
> 
> -- 
> Ville Syrjälä
> Intel