drm/i915: Flip the sense of AGPBUSY_DIS bit

My Gen3 Bspec lists the AGPBUSY# bit in INSTPM as an enable bit rather
than a disable bit. Our code has the opposite idea. Make the code match
the spec.

Might fix some gen3 C3 related interrupt delivery problems. Untested
due to lack of hardware.

v2: call it AGPBUSY_INT_EN to make it clearer it has to do with interrupts

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_reg.h

@@ -1179,7 +1179,7 @@ enum punit_power_well {
 #define   I915_ERROR_INSTRUCTION			(1<<0)
 #define INSTPM	        0x020c0
 #define   INSTPM_SELF_EN (1<<12) /* 915GM only */
-#define   INSTPM_AGPBUSY_DIS (1<<11) /* gen3: when disabled, pending interrupts
+#define   INSTPM_AGPBUSY_INT_EN (1<<11) /* gen3: when disabled, pending interrupts
 					will not assert AGPBUSY# and will only
 					be delivered when out of C3. */
 #define   INSTPM_FORCE_ORDERING				(1<<7) /* GEN6+ */

drivers/gpu/drm/i915/intel_pm.c

@@ -5506,7 +5506,7 @@ static void gen3_init_clock_gating(struct drm_device *dev)
 	I915_WRITE(ECOSKPD, _MASKED_BIT_DISABLE(ECO_FLIP_DONE));
 
 	/* interrupts should cause a wake up from C3 */
-	I915_WRITE(INSTPM, _MASKED_BIT_DISABLE(INSTPM_AGPBUSY_DIS));
+	I915_WRITE(INSTPM, _MASKED_BIT_ENABLE(INSTPM_AGPBUSY_INT_EN));
 }
 
 static void i85x_init_clock_gating(struct drm_device *dev)