drm/i915/fbc: fix FBC_COMPRESSION_MASK on BDW+

Its size is 11:0 instead of 10:0. Found by inspecting the spec. I'm
not aware of any real-world IGT failures caused by this.
Signed-off-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1477065346-13736-2-git-send-email-paulo.r.zanoni@intel.com

drivers/gpu/drm/i915/i915_debugfs.c

@@ -1683,11 +1683,13 @@ static int i915_fbc_status(struct seq_file *m, void *unused)
 		seq_printf(m, "FBC disabled: %s\n",
 			   dev_priv->fbc.no_fbc_reason);
 
-	if (intel_fbc_is_active(dev_priv) &&
-	    INTEL_GEN(dev_priv) >= 7)
+	if (intel_fbc_is_active(dev_priv) && INTEL_GEN(dev_priv) >= 7) {
+		uint32_t mask = INTEL_GEN(dev_priv) >= 8 ?
+				BDW_FBC_COMPRESSION_MASK :
+				IVB_FBC_COMPRESSION_MASK;
 		seq_printf(m, "Compressing: %s\n",
-			   yesno(I915_READ(FBC_STATUS2) &
-				 FBC_COMPRESSION_MASK));
+			   yesno(I915_READ(FBC_STATUS2) & mask));
+	}
 
 	mutex_unlock(&dev_priv->fbc.lock);
 	intel_runtime_pm_put(dev_priv);

drivers/gpu/drm/i915/i915_reg.h

@@ -2188,8 +2188,9 @@ enum skl_disp_power_wells {
 #define FBC_FENCE_OFF		_MMIO(0x3218) /* BSpec typo has 321Bh */
 #define FBC_TAG(i)		_MMIO(0x3300 + (i) * 4)
 
-#define FBC_STATUS2		_MMIO(0x43214)
-#define  FBC_COMPRESSION_MASK	0x7ff
+#define FBC_STATUS2			_MMIO(0x43214)
+#define  IVB_FBC_COMPRESSION_MASK	0x7ff
+#define  BDW_FBC_COMPRESSION_MASK	0xfff
 
 #define FBC_LL_SIZE		(1536)