--- drmP.h	(revision 274286)
+++ drmP.h	(working copy)
@@ -1070,6 +1070,9 @@ 
 extern unsigned int drm_timestamp_precision;
 extern unsigned int drm_timestamp_monotonic;
 
+extern unsigned int drm_force_sclk;
+extern unsigned int drm_force_mclk;
+
 /* Device setup support (drm_drv.c) */
 int	drm_probe(device_t kdev, drm_pci_id_list_t *idlist);
 int	drm_attach(device_t kdev, drm_pci_id_list_t *idlist);
--- drm_drv.c	(revision 274286)
+++ drm_drv.c	(working copy)
@@ -56,6 +56,9 @@ 
 unsigned int drm_vblank_offdelay = 5000;    /* Default to 5000 msecs. */
 unsigned int drm_timestamp_precision = 20;  /* Default to 20 usecs. */
 
+unsigned int drm_force_sclk = 0;            /* MHz units */
+unsigned int drm_force_mclk = 0;            /* MHz units */
+
 /*
  * Default to use monotonic timestamps for wait-for-vblank and page-flip
  * complete events.
@@ -77,6 +80,8 @@ 
 	case MOD_LOAD:
 		TUNABLE_INT_FETCH("drm.debug", &drm_debug_flag);
 		TUNABLE_INT_FETCH("drm.notyet", &drm_notyet_flag);
+		TUNABLE_INT_FETCH("drm.force_sclk", &drm_force_sclk);
+		TUNABLE_INT_FETCH("drm.force_mclk", &drm_force_mclk);
 		break;
 	}
 	return (0);
--- radeon/radeon_device.c	(revision 274286)
+++ radeon/radeon_device.c	(working copy)
@@ -1138,6 +1138,15 @@ 
 	if (r)
 		return r;
 
+	if (drm_force_sclk > 0) {
+		rdev->pm.default_sclk = drm_force_sclk * 100;
+		radeon_set_engine_clock(rdev, rdev->pm.default_sclk);
+	}
+	if (drm_force_mclk > 0) {
+		rdev->pm.default_mclk = drm_force_mclk * 100;
+		radeon_set_memory_clock(rdev, rdev->pm.default_mclk);
+	}
+
 	r = radeon_ib_ring_tests(rdev);
 	if (r)
 		DRM_ERROR("ib ring test failed (%d).\n", r);