diff --git a/shared-core/radeon_cp.c b/shared-core/radeon_cp.c
index ccb0023f..54763fc5 100644
--- a/shared-core/radeon_cp.c
+++ b/shared-core/radeon_cp.c
@@ -1258,6 +1258,12 @@ static void radeon_test_writeback(drm_radeon_private_t * dev_priv)
 		dev_priv->writeback_works = 0;
 		DRM_INFO("writeback forced off\n");
 	}
+
+	if (!dev_priv->writeback_works) {
+		/* Disable writeback to avoid unnecessary bus master transfers */
+		RADEON_WRITE(RADEON_CP_RB_CNTL, RADEON_READ(RADEON_CP_RB_CNTL) | RADEON_RB_NO_UPDATE);
+		RADEON_WRITE(RADEON_SCRATCH_UMSK, 0);
+	}
 }
 
 /* Enable or disable PCI-E GART on the chip */
diff --git a/shared-core/radeon_drv.h b/shared-core/radeon_drv.h
index 441c2976..25ce40c3 100644
--- a/shared-core/radeon_drv.h
+++ b/shared-core/radeon_drv.h
@@ -679,6 +679,7 @@ extern int r300_do_cp_cmdbuf(drm_device_t *dev, DRMFILE filp,
 #define RADEON_CP_RB_BASE		0x0700
 #define RADEON_CP_RB_CNTL		0x0704
 #	define RADEON_BUF_SWAP_32BIT		(2 << 16)
+#	define RADEON_RB_NO_UPDATE		(1 << 27)
 #define RADEON_CP_RB_RPTR_ADDR		0x070c
 #define RADEON_CP_RB_RPTR		0x0710
 #define RADEON_CP_RB_WPTR		0x0714