[Intel-gfx] [PATCH 5/5] drm/i915: Implement Link Rate fallback on Link training failure

[Manasi Navare]

On Fri, Nov 11, 2016 at 11:41:22AM +0200, Jani Nikula wrote:
> On Thu, 10 Nov 2016, Daniel Vetter <daniel at ffwll.ch> wrote:
> > On Wed, Nov 09, 2016 at 08:42:08PM -0800, Manasi Navare wrote:
> >> @@ -5692,6 +5751,39 @@ static bool intel_edp_init_connector(struct intel_dp *intel_dp,
> >>  	return false;
> >>  }
> >>  
> >> +static void intel_dp_modeset_retry_work_fn(struct work_struct *work)
> >> +{
> >> +	struct intel_connector *intel_connector;
> >> +	struct drm_connector *connector;
> >> +	struct drm_display_mode *mode;
> >> +	bool verbose_prune = true;
> >> +
> >> +	intel_connector = container_of(work, typeof(*intel_connector),
> >> +				       modeset_retry_work);
> >> +	connector = &intel_connector->base;
> >> +
> >> +	/* Grab the locks before changing connector property*/
> >> +	mutex_lock(&connector->dev->mode_config.mutex);
> >> +	DRM_DEBUG_KMS("[CONNECTOR:%d:%s]\n", connector->base.id,
> >> +		      connector->name);
> >> +	list_for_each_entry(mode, &connector->modes, head) {
> >> +		mode->status = intel_dp_mode_valid(connector,
> >> +						   mode);
> >> +	}
> >> +	drm_mode_prune_invalid(connector->dev, &connector->modes,
> >> +			       verbose_prune);
> >> +
> >> +	/* Set connector link status to BAD and send a Uevent to notify
> >> +	 * userspace to do a modeset.
> >> +	 */
> >> +	intel_dp_set_link_status_property(connector,
> >> +					  DRM_MODE_LINK_STATUS_BAD);
> >> +	mutex_unlock(&connector->dev->mode_config.mutex);
> >> +
> >> +	/* Send Hotplug uevent so userspace can reprobe */
> >> +	drm_kms_helper_hotplug_event(connector->dev);
> >
> > One downside of keeping all the signalling logic here in i915 is that we
> > don't have a good spot to put the kerneldoc for this new link status
> > property within drm_connector.c for others to easily spot. My suggestion
> > would be to extract function with the following rough pseudo-code:
> 
> Thanks for this. I wanted Manasi to keep the work struct and function
> within i915, but I fell short of coming up with this division.
> 
> BR,
> Jani.
> 
>

Jani, so we ar elooking at two functions going in core,
1. that does mode validation and pruning
2. set link status property

These should be in a separate patch right after declaring the
drm connector property, what do you think?

Regards
Manasi

 
> 
> >
> > drm_connector_set_link_status(connector, status)
> > {
> > 	mutex_lock(mode_config.mutex);
> >
> > 	/* what intel_dp_set_link_status_property() does */
> > 	
> > 	mutex_unlock(mode_config.mutex);
> > 	drm_kms_helper_hotplug_event()
> > }
> >
> > Within intel_dp_modeset_retry_work_fn we'd then first need to drop the
> > lock, and then call this function. The lock drop&reacquire is a bit ugly,
> > but:
> > - it doesn't matter from a performance pov, this is a slow, asynchronous
> >   work.
> > - it doesn't matter for correctnes, the only thing we need is to drop the
> >   lock before calling drm_kms_helper_hotplug_event, and that we update the
> >   link status and the mode list before that too.
> > - long term I expect that properties will get separate locks to protect
> >   their values, and restrict mode_config.mutex to just mode probing. Which
> >   means drm_connnector_set_link_status will use a different lock anyway.
> > - it nicely encapsulates stuff imo.
> >
> > Kerneldoc for drm_connector_set_link_status should mention that this needs
> > to be run from some async work item, and ofc have the full explanation
> > (maybe even quote some pseudo-code, see e.g. drm_modeset_lock.c comments)
> > of how this should be used.
> >
> > Since this is late-stage polish definitely wait for more feedback and for
> > the design to fully settle first.
> > -Daniel
> 
> -- 
> Jani Nikula, Intel Open Source Technology Center
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