drm/i915: only enable sdvo hotplug irq if needed

commit fcbc50da upstream.

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>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/gpu/drm/i915/intel_sdvo.c

@@ -2556,7 +2556,6 @@ bool intel_sdvo_init(struct drm_device *dev, int sdvo_reg)
 		hotplug_mask = IS_SDVOB(sdvo_reg) ?
 			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);
 
@@ -2564,14 +2563,6 @@ bool intel_sdvo_init(struct drm_device *dev, int sdvo_reg)
 	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 SDVO%c\n",
@@ -2579,6 +2570,12 @@ bool intel_sdvo_init(struct drm_device *dev, int sdvo_reg)
 		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. */