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

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Message-ID: <1500513858.21694.13.camel@dk-H97M-D3H>
Date:   Thu, 20 Jul 2017 01:04:12 +0000
From:   "Pandiyan, Dhinakaran" <dhinakaran.pandiyan@...el.com>
To:     "paul.kocialkowski@...ux.intel.com" 
        <paul.kocialkowski@...ux.intel.com>
CC:     "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Vetter, Daniel" <daniel.vetter@...el.com>,
        "airlied@...ux.ie" <airlied@...ux.ie>
Subject: Re: [Intel-gfx] [PATCH] drm/i915: Synchronize connectors states
 when switching from poll to irq


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. 

Some questions so that I understand this better. How short would this
have to be for detect to not complete? Is there a way I can easily test
this scenario?

> 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.
> 

Not sure I understand this correctly, looks like you are setting the
event_bits even if there was no irq during the polling interval. Is that
right?


> Without this, no irq will be triggered and the hpd change will be lost.
> 
> Signed-off-by: Paul Kocialkowski <paul.kocialkowski@...ux.intel.com>
> ---
>  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) {
> -				if (connector->polled != intel_connector->polled)
> +				if (connector->polled != intel_connector->polled) {
>  					DRM_DEBUG_DRIVER("Reenabling HPD on connector %s\n",
>  							 connector->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);

How does this work with DP connectors? From what I understand, the
event_bits are set for DP based on the return value from
intel_dp_hpd_pulse(). But, doesn't this patch set the bits
unconditionally?

> +
>  	intel_runtime_pm_put(dev_priv);
>  }
>