[PATCH v2] drm/i915: intel_hpd_init(): Fix suspend/resume reprobing

[Lyude]

This fixes reprobing of display connectors on resume. 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
	  connectors.
	- 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 for that one.

In addition, we now avoid setting connector->polled to
DRM_CONNECTOR_POLL_HPD for MST connectors, since their reprobing is handled
by the mst helpers. This is probably what was originally intended to happen
here anyway.

Fixes: 0e32b39ceed6 ("drm/i915: add DP 1.2 MST support (v0.7)")
Cc: stable at vger.kernel.org
Signed-off-by: Lyude <cpaul at redhat.com>
---
				    Changes
* Use the explanation of the issue as the commit message instead
* Change the title of the commit, since this does more then just stop a check
  for an encoder now
* Add "Fixes" line for the patch that introduced this regression
* Don't enable DRM_CONNECTOR_POLL_HPD for mst connectors

 drivers/gpu/drm/i915/intel_hotplug.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_hotplug.c b/drivers/gpu/drm/i915/intel_hotplug.c
index b177857..51ecf0b4 100644
--- a/drivers/gpu/drm/i915/intel_hotplug.c
+++ b/drivers/gpu/drm/i915/intel_hotplug.c
@@ -468,9 +468,9 @@ 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)
-			connector->polled = DRM_CONNECTOR_POLL_HPD;
-		if (intel_connector->mst_port)
+		if (!connector->polled && !intel_connector->mst_port &&
+		    I915_HAS_HOTPLUG(dev) &&
+		    intel_connector->encoder->hpd_pin > HPD_NONE)
 			connector->polled = DRM_CONNECTOR_POLL_HPD;
 	}
 
-- 
2.5.0