drm/radeon: do a posting read in si_set_irq

commit 0586915e upstream.

To make sure the writes go through the pci bridge.

bug:
https://bugzilla.kernel.org/show_bug.cgi?id=90741Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Zefan Li <lizefan@huawei.com>

drivers/gpu/drm/radeon/si.c

@@ -4126,6 +4126,9 @@ int si_init(struct radeon_device *rdev)
 		return -EINVAL;
 	}
 
+	/* posting read */
+	RREG32(SRBM_STATUS);
+
 	return 0;
 }