drm/i915: Ignore GTFIFODBG FIFO free entry fields on CHV

On CHV GTFIFODBG has some read-only bits to indicate the number
of free FIFO entries. Ignore these when checking to see if any
of the sticky error bits are set.

This gets rid of these during device resume:
[drm:cherryview_enable_rps] GT fifo had a previous error 1080000

While at it, move the assignments out of the if().

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/1460570970-14073-1-git-send-email-ville.syrjala@linux.intel.com
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_reg.h

@@ -6866,6 +6866,8 @@ enum skl_disp_power_wells {
 #define  VLV_SPAREG2H				_MMIO(0xA194)
 
 #define  GTFIFODBG				_MMIO(0x120000)
+#define    GT_FIFO_SBDEDICATE_FREE_ENTRY_CHV	(0x1f << 20)
+#define    GT_FIFO_FREE_ENTRIES_CHV		(0x7f << 13)
 #define    GT_FIFO_SBDROPERR			(1<<6)
 #define    GT_FIFO_BLOBDROPERR			(1<<5)
 #define    GT_FIFO_SB_READ_ABORTERR		(1<<4)

drivers/gpu/drm/i915/intel_pm.c

@@ -4997,7 +4997,8 @@ static void gen6_enable_rps(struct drm_device *dev)
 	I915_WRITE(GEN6_RC_STATE, 0);
 
 	/* Clear the DBG now so we don't confuse earlier errors */
-	if ((gtfifodbg = I915_READ(GTFIFODBG))) {
+	gtfifodbg = I915_READ(GTFIFODBG);
+	if (gtfifodbg) {
 		DRM_ERROR("GT fifo had a previous error %x\n", gtfifodbg);
 		I915_WRITE(GTFIFODBG, gtfifodbg);
 	}
@@ -5528,7 +5529,8 @@ static void cherryview_enable_rps(struct drm_device *dev)
 
 	WARN_ON(!mutex_is_locked(&dev_priv->rps.hw_lock));
 
-	gtfifodbg = I915_READ(GTFIFODBG);
+	gtfifodbg = I915_READ(GTFIFODBG) & ~(GT_FIFO_SBDEDICATE_FREE_ENTRY_CHV |
+					     GT_FIFO_FREE_ENTRIES_CHV);
 	if (gtfifodbg) {
 		DRM_DEBUG_DRIVER("GT fifo had a previous error %x\n",
 				 gtfifodbg);
@@ -5627,7 +5629,8 @@ static void valleyview_enable_rps(struct drm_device *dev)
 
 	valleyview_check_pctx(dev_priv);
 
-	if ((gtfifodbg = I915_READ(GTFIFODBG))) {
+	gtfifodbg = I915_READ(GTFIFODBG);
+	if (gtfifodbg) {
 		DRM_DEBUG_DRIVER("GT fifo had a previous error %x\n",
 				 gtfifodbg);
 		I915_WRITE(GTFIFODBG, gtfifodbg);