drm/i915: Don't call intel_get_hpd_pins() when there's no hotplug interrupt

On GMCH plaforms we are now getting the following spew on aux
interrupts:
[drm:intel_get_hpd_pins] hotplug event received, stat 0x00000000, dig 0x00000000, pins 0x00000000
[drm:intel_get_hpd_pins] hotplug event received, stat 0x00000000, dig 0x00000000, pins 0x00000000
[drm:intel_get_hpd_pins] hotplug event received, stat 0x00000000, dig 0x00000000, pins 0x00000000
[drm:intel_get_hpd_pins] hotplug event received, stat 0x00000000, dig 0x00000000, pins 0x00000000
[drm:intel_get_hpd_pins] hotplug event received, stat 0x00000000, dig 0x00000000, pins 0x00000000
[drm:intel_dp_aux_ch] dp_aux_ch timeout status 0x71450064

Prevent it by not calling intel_get_hpd_pins() unless one of the HPD
interrupt bits are actually set.

I already fixed similar annoyance once with
4bca26d0 drm/i915: Use HOTPLUG_INT_STATUS_G4X on VLV/CHV

but another source for it got added in
fd63e2a9 drm/i915: combine i9xx_get_hpd_pins and pch_get_hpd_pins

due to pch_get_hpd_pins() being chosen over i9xx_get_hpd_pins() to
serve as the new unified piece of code. pch_get_hpd_pins() had the debug
print, and i9xx_get_hpd_pins() didn't.

Cc: Imre Deak <imre.deak@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_irq.c

@@ -1639,20 +1639,26 @@ static void i9xx_hpd_irq_handler(struct drm_device *dev)
 	if (IS_G4X(dev) || IS_VALLEYVIEW(dev)) {
 		u32 hotplug_trigger = hotplug_status & HOTPLUG_INT_STATUS_G4X;
 
-		intel_get_hpd_pins(&pin_mask, &long_mask, hotplug_trigger,
-				   hotplug_trigger, hpd_status_g4x,
-				   i9xx_port_hotplug_long_detect);
-		intel_hpd_irq_handler(dev, pin_mask, long_mask);
+		if (hotplug_trigger) {
+			intel_get_hpd_pins(&pin_mask, &long_mask, hotplug_trigger,
+					   hotplug_trigger, hpd_status_g4x,
+					   i9xx_port_hotplug_long_detect);
+
+			intel_hpd_irq_handler(dev, pin_mask, long_mask);
+		}
 
 		if (hotplug_status & DP_AUX_CHANNEL_MASK_INT_STATUS_G4X)
 			dp_aux_irq_handler(dev);
 	} else {
 		u32 hotplug_trigger = hotplug_status & HOTPLUG_INT_STATUS_I915;
 
-		intel_get_hpd_pins(&pin_mask, &long_mask, hotplug_trigger,
-				   hotplug_trigger, hpd_status_g4x,
-				   i9xx_port_hotplug_long_detect);
-		intel_hpd_irq_handler(dev, pin_mask, long_mask);
+		if (hotplug_trigger) {
+			intel_get_hpd_pins(&pin_mask, &long_mask, hotplug_trigger,
+					   hotplug_trigger, hpd_status_g4x,
+					   i9xx_port_hotplug_long_detect);
+
+			intel_hpd_irq_handler(dev, pin_mask, long_mask);
+		}
 	}
 }