drm/radeon/kms: fix regression rendering issue on R6XX/R7XX

It seems that some R6XX/R7XX silently ignore HDP flush when
programmed through ring, this patch addback an ioctl callback
to allow R6XX/R7XX hw to perform such flush through MMIO in
order to fix a regression. For more details see:

http://bugzilla.kernel.org/show_bug.cgi?id=15186

Signed-off-by: Jerome Glisse <jglisse@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/radeon/radeon.h b/drivers/gpu/drm/radeon/radeon.h
index 2d5f2bf..37150fc 100644
--- a/drivers/gpu/drm/radeon/radeon.h
+++ b/drivers/gpu/drm/radeon/radeon.h
@@ -661,6 +661,13 @@
 	void (*hpd_fini)(struct radeon_device *rdev);
 	bool (*hpd_sense)(struct radeon_device *rdev, enum radeon_hpd_id hpd);
 	void (*hpd_set_polarity)(struct radeon_device *rdev, enum radeon_hpd_id hpd);
+	/* ioctl hw specific callback. Some hw might want to perform special
+	 * operation on specific ioctl. For instance on wait idle some hw
+	 * might want to perform and HDP flush through MMIO as it seems that
+	 * some R6XX/R7XX hw doesn't take HDP flush into account if programmed
+	 * through ring.
+	 */
+	void (*ioctl_wait_idle)(struct radeon_device *rdev, struct radeon_bo *bo);
 };
 
 /*