Index: shared-core/radeon_cp.c
===================================================================
RCS file: /cvs/dri/drm/shared-core/radeon_cp.c,v
retrieving revision 1.76
diff -p -u -r1.76 radeon_cp.c
--- shared-core/radeon_cp.c	18 May 2006 07:32:37 -0000	1.76
+++ shared-core/radeon_cp.c	14 Jun 2006 08:46:39 -0000
@@ -1258,6 +1280,12 @@ static void radeon_test_writeback(drm_ra
 		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 */
Index: shared-core/radeon_drv.h
===================================================================
RCS file: /cvs/dri/drm/shared-core/radeon_drv.h,v
retrieving revision 1.71
diff -p -u -r1.71 radeon_drv.h
--- shared-core/radeon_drv.h	24 May 2006 18:36:24 -0000	1.71
+++ shared-core/radeon_drv.h	14 Jun 2006 08:46:40 -0000
@@ -679,6 +686,7 @@ extern int r300_do_cp_cmdbuf(drm_device_
 #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