diff --git a/drivers/gpu/drm/radeon/r300.c b/drivers/gpu/drm/radeon/r300.c
index 36b4f7b..23fee54 100644
--- a/drivers/gpu/drm/radeon/r300.c
+++ b/drivers/gpu/drm/radeon/r300.c
@@ -745,6 +745,11 @@
 		break;
 	case 0x4E00:
 		/* RB3D_CCTL */
+		if ((idx_value & (1 << 10)) && /* CMASK_ENABLE */
+		    p->rdev->cmask_filp != p->filp) {
+			DRM_ERROR("Invalid RB3D_CCTL: Cannot enable CMASK.\n");
+			return -EINVAL;
+		}
 		track->num_cb = ((idx_value >> 5) & 0x3) + 1;
 		break;
 	case 0x4E38:
@@ -1206,6 +1211,10 @@
 		if (p->rdev->hyperz_filp != p->filp)
 			return -EINVAL;
 		break;
+	case PACKET3_3D_CLEAR_CMASK:
+		if (p->rdev->cmask_filp != p->filp)
+			return -EINVAL;
+		break;
 	case PACKET3_NOP:
 		break;
 	default:
diff --git a/drivers/gpu/drm/radeon/r300d.h b/drivers/gpu/drm/radeon/r300d.h
index 0c036c6..1f519a5 100644
--- a/drivers/gpu/drm/radeon/r300d.h
+++ b/drivers/gpu/drm/radeon/r300d.h
@@ -54,6 +54,7 @@
 #define		PACKET3_3D_DRAW_IMMD_2		0x35
 #define		PACKET3_3D_DRAW_INDX_2		0x36
 #define		PACKET3_3D_CLEAR_HIZ		0x37
+#define		PACKET3_3D_CLEAR_CMASK		0x38
 #define		PACKET3_BITBLT_MULTI		0x9B
 
 #define PACKET0(reg, n)	(CP_PACKET0 |					\
diff --git a/drivers/gpu/drm/radeon/radeon.h b/drivers/gpu/drm/radeon/radeon.h
index 140eace..a835d95 100644
--- a/drivers/gpu/drm/radeon/radeon.h
+++ b/drivers/gpu/drm/radeon/radeon.h
@@ -1168,8 +1168,9 @@
 	uint8_t			audio_category_code;
 
 	struct notifier_block acpi_nb;
-	/* only one userspace can use Hyperz features at a time */
+	/* only one userspace can use Hyperz features or CMASK at a time */
 	struct drm_file *hyperz_filp;
+	struct drm_file *cmask_filp;
 	/* i2c buses */
 	struct radeon_i2c_chan *i2c_bus[RADEON_MAX_I2C_BUS];
 };
diff --git a/drivers/gpu/drm/radeon/radeon_drv.c b/drivers/gpu/drm/radeon/radeon_drv.c
index 18225f2..be5cb4f 100644
--- a/drivers/gpu/drm/radeon/radeon_drv.c
+++ b/drivers/gpu/drm/radeon/radeon_drv.c
@@ -48,7 +48,7 @@
  * - 2.5.0 - add get accel 2 to work around ddx breakage for evergreen
  * - 2.6.0 - add tiling config query (r6xx+), add initial HiZ support (r300->r500)
  *   2.7.0 - fixups for r600 2D tiling support. (no external ABI change), add eg dyn gpr regs
- *   2.8.0 - pageflip support, r500 US_FORMAT regs. r500 ARGB2101010 colorbuf
+ *   2.8.0 - pageflip support, r500 US_FORMAT regs. r500 ARGB2101010 colorbuf, r300->r500 CMASK
  */
 #define KMS_DRIVER_MAJOR	2
 #define KMS_DRIVER_MINOR	8
diff --git a/drivers/gpu/drm/radeon/radeon_kms.c b/drivers/gpu/drm/radeon/radeon_kms.c
index b268633..28a53e4a 100644
--- a/drivers/gpu/drm/radeon/radeon_kms.c
+++ b/drivers/gpu/drm/radeon/radeon_kms.c
@@ -96,9 +96,27 @@
 	return r;
 }
 
+static void radeon_set_filp_rights(struct drm_device *dev,
+				   struct drm_file **owner,
+				   struct drm_file *applier,
+				   uint32_t *value)
+{
+	mutex_lock(&dev->struct_mutex);
+	if (*value == 1) {
+		/* wants rights */
+		if (!*owner)
+			*owner = applier;
+	} else if (*value == 0) {
+		/* revokes rights */
+		if (*owner == applier)
+			*owner = NULL;
+	}
+	*value = *owner == applier ? 1 : 0;
+	mutex_unlock(&dev->struct_mutex);
+}
 
 /*
- * Userspace get informations ioctl
+ * Userspace get information ioctl
  */
 int radeon_info_ioctl(struct drm_device *dev, void *data, struct drm_file *filp)
 {
@@ -173,18 +191,15 @@
 			DRM_DEBUG_KMS("WANT_HYPERZ: invalid value %d\n", value);
 			return -EINVAL;
 		}
-		mutex_lock(&dev->struct_mutex);
-		if (value == 1) {
-			/* wants hyper-z */
-			if (!rdev->hyperz_filp)
-				rdev->hyperz_filp = filp;
-		} else if (value == 0) {
-			/* revokes hyper-z */
-			if (rdev->hyperz_filp == filp)
-				rdev->hyperz_filp = NULL;
+		radeon_set_filp_rights(dev, &rdev->hyperz_filp, filp, &value);
+		break;
+	case RADEON_INFO_WANT_CMASK:
+		/* The same logic as Hyper-Z. */
+		if (value >= 2) {
+			DRM_DEBUG_KMS("WANT_CMASK: invalid value %d\n", value);
+			return -EINVAL;
 		}
-		value = rdev->hyperz_filp == filp ?  1 : 0;
-		mutex_unlock(&dev->struct_mutex);
+		radeon_set_filp_rights(dev, &rdev->cmask_filp, filp, &value);
 		break;
 	default:
 		DRM_DEBUG_KMS("Invalid request %d\n", info->request);
diff --git a/include/drm/radeon_drm.h b/include/drm/radeon_drm.h
index 10f8b53..e95a86b 100644
--- a/include/drm/radeon_drm.h
+++ b/include/drm/radeon_drm.h
@@ -906,6 +906,7 @@
 #define RADEON_INFO_ACCEL_WORKING2	0x05
 #define RADEON_INFO_TILING_CONFIG	0x06
 #define RADEON_INFO_WANT_HYPERZ		0x07
+#define RADEON_INFO_WANT_CMASK		0x08 /* get access to CMASK on r300 */
 
 struct drm_radeon_info {
 	uint32_t		request;