linux-kernel - Re: [PATCH] drm/i915: Synchronize connectors states when switching from poll to irq

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Date:   Thu, 20 Jul 2017 17:41:13 +0300
From:   Paul Kocialkowski <paul.kocialkowski@...ux.intel.com>
To:     Manasi Navare <manasi.d.navare@...el.com>
Cc:     intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        Daniel Vetter <daniel.vetter@...el.com>
Subject: Re: [PATCH] drm/i915: Synchronize connectors states when switching
 from poll to irq

On Wed, 2017-07-19 at 23:11 -0700, Manasi Navare wrote:
> On Tue, Jul 18, 2017 at 03:11:42PM +0300, Paul Kocialkowski wrote:
> > On Mon, 2017-06-26 at 15:32 +0300, Paul Kocialkowski wrote:
> > > After detecting an IRQ storm, hotplug detection will switch from
> > > irq-based detection to poll-based detection. After a short delay
> > > or
> > > when resetting storm detection from debugfs, detection will switch
> > > back to being irq-based.
> > > 
> > > However, it may occur that polling does not have enough time to
> > > detect
> > > the current connector state when that second switch takes place.
> > > Thus,
> > > this sets the appropriate hotplug event bits for the concerned
> > > connectors and schedules the hotplug work, that will ensure the
> > > connectors states are in sync when switching back to irq.
> > > 
> > > Without this, no irq will be triggered and the hpd change will be
> > > lost.
> > 
> > Does anyone have feedback to provide on this?
> > It looks like it should be a no-brainer.
> > 
> > Cheers,
> > 
> > Paul
> > 
> > > Signed-off-by: Paul Kocialkowski <paul.kocialkowski@...ux.intel.co
> > > m>
> > > ---
> > >  drivers/gpu/drm/i915/intel_hotplug.c | 8 +++++++-
> > >  1 file changed, 7 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/intel_hotplug.c
> > > b/drivers/gpu/drm/i915/intel_hotplug.c
> > > index f1200272a699..29f55480b0bb 100644
> > > --- a/drivers/gpu/drm/i915/intel_hotplug.c
> > > +++ b/drivers/gpu/drm/i915/intel_hotplug.c
> > > @@ -218,9 +218,13 @@ static void
> > > intel_hpd_irq_storm_reenable_work(struct work_struct *work)
> > >  			struct intel_connector *intel_connector =
> > > to_intel_connector(connector);
> > >  
> > >  			if (intel_connector->encoder->hpd_pin ==
> > > i) {
> 
> So if this hpd pin in intel_connector->encoder is set then that
> means it got the hpd but because connector->polled is !=
> intel_connector->polled
> polling didnt detect that connector.
>
> Is that what you are trying to do here?

The first test is simply a way to match the intel_connector to the drm
connector. The second one indicates whether we are using polling or irq
mode. If they don't match (given the test earlier in the code that only
selects hpd pins that use irq mode), it means that we are switching from
 polling mode to irq mode.

When that happens, it is necessary to assume that the connector state
may have changed (in the time window between the last poll and enabling
irq), so the hotplug work is scheduled. It will check whether a hpd
state change did happen or not and issue a uevent if that is the case.

> > > -				if (connector->polled !=
> > > intel_connector->polled)
> > > +				if (connector->polled !=
> > > intel_connector->polled) {
> > >  					DRM_DEBUG_DRIVER("Reenabl
> > > ing
> > > HPD on connector %s\n",
> > >  							 connecto
> > > r-
> > > > name);
> > > 
> > > +
> > > +					dev_priv-
> > > >hotplug.event_bits
> > > > = (1 << i);
> > > 
> > > +				}
> > > +
> > >  				connector->polled =
> > > intel_connector-
> > > > polled;
> > > 
> > >  				if (!connector->polled)
> > >  					connector->polled =
> > > DRM_CONNECTOR_POLL_HPD;
> > > @@ -232,6 +236,8 @@ static void
> > > intel_hpd_irq_storm_reenable_work(struct work_struct *work)
> > >  		dev_priv->display.hpd_irq_setup(dev_priv);
> > >  	spin_unlock_irq(&dev_priv->irq_lock);
> > >  
> > > +	schedule_work(&dev_priv->hotplug.hotplug_work);
> > > +
> > >  	intel_runtime_pm_put(dev_priv);
> > >  }
> > >  
> > 
> > -- 
> > Paul Kocialkowski <paul.kocialkowski@...ux.intel.com>
> > Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo,
> > Finland
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@...ts.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
-- 
Paul Kocialkowski <paul.kocialkowski@...ux.intel.com>
Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo, Finland

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