linux-kernel - Re: [Intel-gfx] [PATCH] drm/i915: intel_hpd_init(): Don't check connectors for an encoder

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Date:	Tue, 5 Jan 2016 21:05:49 +0100
From:	Daniel Vetter <daniel@...ll.ch>
To:	Lyude <cpaul@...hat.com>
Cc:	Daniel Vetter <daniel.vetter@...el.com>,
	Jani Nikula <jani.nikula@...ux.intel.com>,
	David Airlie <airlied@...ux.ie>,
	intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org,
	Benjamin Tissoires <btissoir@...hat.com>
Subject: Re: [Intel-gfx] [PATCH] drm/i915: intel_hpd_init(): Don't check
 connectors for an encoder

On Tue, Jan 05, 2016 at 02:53:08PM -0500, Lyude wrote:
> There's no reason to check for an active encoder when setting up hpd,
> especially since a disconnected connector isn't going to have an encoder
> in the first place. This fixes reprobing display connectors on resume.
> 
> Signed-off-by: Lyude <cpaul@...hat.com>
> ---
> After some talking with danvet on IRC, I learned that calling
> drm_helper_hpd_irq_event() does actually trigger a full reprobe of each
> connector's status. It turns out this is the actual reason reprobing on resume
> hasn't been working (this was observed on a T440s):
> 
> 	- We call hpd_init()
> 	- We check each connector for a couple of things before marking
> 	  connector->polled with DRM_CONNECTOR_POLL_HPD, one of which is an
> 	  active encoder. Of course, a disconnected port won't have an active
> 	  encoder, so we don't add the flag to any of the connector's.
> 	- We call drm_helper_hpd_irq_event()
> 	- drm_helper_irq_event() checks each connector for the
> 	  DRM_CONNECTOR_POLL_HPD flag. The only one that has it is eDP-1, so we
> 	  skip reprobing each connector except that one.

The above explanation should be part of the commit message, otherwise it's
hard to understand the impact of this fix.

Fixes: 0e32b39ceed6 ("drm/i915: add DP 1.2 MST support (v0.7)")
Cc: stable@...r.kernel.org

Unfortunately Dave doesn't explain in his MST commit why he's done this.
Dave? I can't come up with a reason, but better to test that. Lyude?

Anyway looks good to me.

Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>

> 
>  drivers/gpu/drm/i915/intel_hotplug.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_hotplug.c b/drivers/gpu/drm/i915/intel_hotplug.c
> index b177857..18797bc 100644
> --- a/drivers/gpu/drm/i915/intel_hotplug.c
> +++ b/drivers/gpu/drm/i915/intel_hotplug.c
> @@ -468,7 +468,7 @@ void intel_hpd_init(struct drm_i915_private *dev_priv)
>  	list_for_each_entry(connector, &mode_config->connector_list, head) {
>  		struct intel_connector *intel_connector = to_intel_connector(connector);
>  		connector->polled = intel_connector->polled;
> -		if (connector->encoder && !connector->polled && I915_HAS_HOTPLUG(dev) && intel_connector->encoder->hpd_pin > HPD_NONE)
> +		if (!connector->polled && I915_HAS_HOTPLUG(dev) && intel_connector->encoder->hpd_pin > HPD_NONE)
>  			connector->polled = DRM_CONNECTOR_POLL_HPD;
>  		if (intel_connector->mst_port)
>  			connector->polled = DRM_CONNECTOR_POLL_HPD;
> -- 
> 2.5.0
> 
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@...ts.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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