drm/i915: only enable sdvo hotplug irq if needed

Avoid constant wakeups caused by noisy irq lines when we don't even care
about the irq. This should be particularly useful for i945g/gm where the
hotplug has been disabled:

commit 768b107e
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Fri May 4 11:29:56 2012 +0200

    drm/i915: disable sdvo hotplug on i945g/gm

v2: While at it, remove the bogus hotplug_active read, and do not mask
hotplug_active[0] before checking whether the irq is needed, per discussion
with Daniel on IRC.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=38442Tested-by: Dominik Köppl <dominik@devwork.org>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_sdvo.c

@@ -2573,7 +2573,6 @@ bool intel_sdvo_init(struct drm_device *dev, uint32_t sdvo_reg, bool is_sdvob)
 		hotplug_mask = intel_sdvo->is_sdvob ?
 			SDVOB_HOTPLUG_INT_STATUS_I915 : SDVOC_HOTPLUG_INT_STATUS_I915;
 	}
-	dev_priv->hotplug_supported_mask |= hotplug_mask;
 
 	drm_encoder_helper_add(&intel_encoder->base, &intel_sdvo_helper_funcs);
 
@@ -2581,14 +2580,6 @@ bool intel_sdvo_init(struct drm_device *dev, uint32_t sdvo_reg, bool is_sdvob)
 	if (!intel_sdvo_get_capabilities(intel_sdvo, &intel_sdvo->caps))
 		goto err;
 
-	/* Set up hotplug command - note paranoia about contents of reply.
-	 * We assume that the hardware is in a sane state, and only touch
-	 * the bits we think we understand.
-	 */
-	intel_sdvo_get_value(intel_sdvo, SDVO_CMD_GET_ACTIVE_HOT_PLUG,
-			     &intel_sdvo->hotplug_active, 2);
-	intel_sdvo->hotplug_active[0] &= ~0x3;
-
 	if (intel_sdvo_output_setup(intel_sdvo,
 				    intel_sdvo->caps.output_flags) != true) {
 		DRM_DEBUG_KMS("SDVO output failed to setup on %s\n",
@@ -2596,6 +2587,12 @@ bool intel_sdvo_init(struct drm_device *dev, uint32_t sdvo_reg, bool is_sdvob)
 		goto err;
 	}
 
+	/* Only enable the hotplug irq if we need it, to work around noisy
+	 * hotplug lines.
+	 */
+	if (intel_sdvo->hotplug_active[0])
+		dev_priv->hotplug_supported_mask |= hotplug_mask;
+
 	intel_sdvo_select_ddc_bus(dev_priv, intel_sdvo, sdvo_reg);
 
 	/* Set the input timing to the screen. Assume always input 0. */