drm/radeon/kms: fix RS600 MC setup.

Again we try to put VRAM at 0, and it didn't work on this chipset,
reports of corrupt RAM appeared on irc and bugzilla.

Fix the vram location according to what the BIOS setup, I'm not 100%
sure we don't need the same thing on rs690/rs780/rs880, we probably
should do it there just in case as its what the DDX does.
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/rs600.c

@@ -45,6 +45,20 @@
 void rs600_gpu_init(struct radeon_device *rdev);
 int rs600_mc_wait_for_idle(struct radeon_device *rdev);
 
+int rs600_mc_init(struct radeon_device *rdev)
+{
+	/* read back the MC value from the hw */
+	uint32_t mc_fb_loc;
+	int r;
+
+	mc_fb_loc = RREG32_MC(R_000004_MC_FB_LOCATION);
+	rdev->mc.vram_location = G_000004_MC_FB_START(mc_fb_loc) << 16;
+	rdev->mc.gtt_location = 0xffffffffUL;
+	r = radeon_mc_setup(rdev);
+	if (r)
+		return r;
+	return 0;
+}
 /*
  * GART.
  */
@@ -505,7 +519,7 @@ int rs600_init(struct radeon_device *rdev)
 	/* Get vram informations */
 	rs600_vram_info(rdev);
 	/* Initialize memory controller (also test AGP) */
-	r = r420_mc_init(rdev);
+	r = rs600_mc_init(rdev);
 	if (r)
 		return r;
 	rs600_debugfs(rdev);