drm/i915: Optimize VLV/CHV display FIFO updates

Use I915_{READ,WRITE}_FW() for updating the DSPARB registers on
VLV/CHV. This is less expesive as we can grab the uncore.lock across
the entire sequence of reads and writes instead of each register
access grabbing it.

This also allows us to eliminate the dsparb lock entirely as the
uncore.lock now effectively protects the contents of the DSPARB
registers.

v2: Add a note that interrupts are already disabled (Chris)

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170309154434.29303-6-ville.syrjala@linux.intel.com
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>

drivers/gpu/drm/i915/i915_drv.c

@@ -825,7 +825,6 @@ static int i915_driver_init_early(struct drm_i915_private *dev_priv,
 
 	spin_lock_init(&dev_priv->mm.object_stat_lock);
 	spin_lock_init(&dev_priv->mmio_flip_lock);
-	spin_lock_init(&dev_priv->wm.dsparb_lock);
 	mutex_init(&dev_priv->sb_lock);
 	mutex_init(&dev_priv->modeset_restore_lock);
 	mutex_init(&dev_priv->av_mutex);

drivers/gpu/drm/i915/i915_drv.h

@@ -2375,9 +2375,6 @@ struct drm_i915_private {
 	} sagv_status;
 
 	struct {
-		/* protects DSPARB registers on pre-g4x/vlv/chv */
-		spinlock_t dsparb_lock;
-
 		/*
 		 * Raw watermark latency values:
 		 * in 0.1us units for WM0,

drivers/gpu/drm/i915/intel_pm.c

@@ -1358,13 +1358,22 @@ static void vlv_atomic_update_fifo(struct intel_atomic_state *state,
 
 	trace_vlv_fifo_size(crtc, sprite0_start, sprite1_start, fifo_size);
 
-	spin_lock(&dev_priv->wm.dsparb_lock);
+	/*
+	 * uncore.lock serves a double purpose here. It allows us to
+	 * use the less expensive I915_{READ,WRITE}_FW() functions, and
+	 * it protects the DSPARB registers from getting clobbered by
+	 * parallel updates from multiple pipes.
+	 *
+	 * intel_pipe_update_start() has already disabled interrupts
+	 * for us, so a plain spin_lock() is sufficient here.
+	 */
+	spin_lock(&dev_priv->uncore.lock);
 
 	switch (crtc->pipe) {
 		uint32_t dsparb, dsparb2, dsparb3;
 	case PIPE_A:
-		dsparb = I915_READ(DSPARB);
-		dsparb2 = I915_READ(DSPARB2);
+		dsparb = I915_READ_FW(DSPARB);
+		dsparb2 = I915_READ_FW(DSPARB2);
 
 		dsparb &= ~(VLV_FIFO(SPRITEA, 0xff) |
 			    VLV_FIFO(SPRITEB, 0xff));
@@ -1376,12 +1385,12 @@ static void vlv_atomic_update_fifo(struct intel_atomic_state *state,
 		dsparb2 |= (VLV_FIFO(SPRITEA_HI, sprite0_start >> 8) |
 			   VLV_FIFO(SPRITEB_HI, sprite1_start >> 8));
 
-		I915_WRITE(DSPARB, dsparb);
-		I915_WRITE(DSPARB2, dsparb2);
+		I915_WRITE_FW(DSPARB, dsparb);
+		I915_WRITE_FW(DSPARB2, dsparb2);
 		break;
 	case PIPE_B:
-		dsparb = I915_READ(DSPARB);
-		dsparb2 = I915_READ(DSPARB2);
+		dsparb = I915_READ_FW(DSPARB);
+		dsparb2 = I915_READ_FW(DSPARB2);
 
 		dsparb &= ~(VLV_FIFO(SPRITEC, 0xff) |
 			    VLV_FIFO(SPRITED, 0xff));
@@ -1393,12 +1402,12 @@ static void vlv_atomic_update_fifo(struct intel_atomic_state *state,
 		dsparb2 |= (VLV_FIFO(SPRITEC_HI, sprite0_start >> 8) |
 			   VLV_FIFO(SPRITED_HI, sprite1_start >> 8));
 
-		I915_WRITE(DSPARB, dsparb);
-		I915_WRITE(DSPARB2, dsparb2);
+		I915_WRITE_FW(DSPARB, dsparb);
+		I915_WRITE_FW(DSPARB2, dsparb2);
 		break;
 	case PIPE_C:
-		dsparb3 = I915_READ(DSPARB3);
-		dsparb2 = I915_READ(DSPARB2);
+		dsparb3 = I915_READ_FW(DSPARB3);
+		dsparb2 = I915_READ_FW(DSPARB2);
 
 		dsparb3 &= ~(VLV_FIFO(SPRITEE, 0xff) |
 			     VLV_FIFO(SPRITEF, 0xff));
@@ -1410,16 +1419,16 @@ static void vlv_atomic_update_fifo(struct intel_atomic_state *state,
 		dsparb2 |= (VLV_FIFO(SPRITEE_HI, sprite0_start >> 8) |
 			   VLV_FIFO(SPRITEF_HI, sprite1_start >> 8));
 
-		I915_WRITE(DSPARB3, dsparb3);
-		I915_WRITE(DSPARB2, dsparb2);
+		I915_WRITE_FW(DSPARB3, dsparb3);
+		I915_WRITE_FW(DSPARB2, dsparb2);
 		break;
 	default:
 		break;
 	}
 
-	POSTING_READ(DSPARB);
+	POSTING_READ_FW(DSPARB);
 
-	spin_unlock(&dev_priv->wm.dsparb_lock);
+	spin_unlock(&dev_priv->uncore.lock);
 }
 
 #undef VLV_FIFO