drm/i915: Move the C3 LP write bit setup to gen3_init_clock_gating() for KMS

Move the MI_ARB_STATE MI_ARB_C3_LP_WRITE_ENABLE setup to
gen3_init_clock_gating() from i915_gem_load() when KMS is enabled. Leave
it in i915_gem_load() for the UMS case, but add an explcit check, just
to make it easier to spot it when we eventually rip out UMS support.

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_gem.c

@@ -4756,7 +4756,7 @@ i915_gem_load(struct drm_device *dev)
 	init_waitqueue_head(&dev_priv->gpu_error.reset_queue);
 
 	/* On GEN3 we really need to make sure the ARB C3 LP bit is set */
-	if (IS_GEN3(dev)) {
+	if (!drm_core_check_feature(dev, DRIVER_MODESET) && IS_GEN3(dev)) {
 		I915_WRITE(MI_ARB_STATE,
 			   _MASKED_BIT_ENABLE(MI_ARB_C3_LP_WRITE_ENABLE));
 	}

drivers/gpu/drm/i915/intel_pm.c

@@ -5507,6 +5507,9 @@ static void gen3_init_clock_gating(struct drm_device *dev)
 
 	/* interrupts should cause a wake up from C3 */
 	I915_WRITE(INSTPM, _MASKED_BIT_ENABLE(INSTPM_AGPBUSY_INT_EN));
+
+	/* On GEN3 we really need to make sure the ARB C3 LP bit is set */
+	I915_WRITE(MI_ARB_STATE, _MASKED_BIT_ENABLE(MI_ARB_C3_LP_WRITE_ENABLE));
 }
 
 static void i85x_init_clock_gating(struct drm_device *dev)