Ok, I managed to get the dmesg output using piglit and the r600.tests, so I
think this confirms 325422c49449acdd8df1eb2ca8ed81f7696c38cc as culprit.

But I think the commit I identified (e110c98cae0ceae47db6cf26c08707505ce92479)
is bad too, because there I only needed to start steam to get the errors.