The problem boils down to the order when the bit11
of the texture size is or'ed to the original width.
In the end each mipmap level has the same width or
height because of that 11 bit is ored to the scaled
down lod with and thus blows up the size again to the
full size or more due to the power of two rounding
afterwards.

The attached patch changes this order so that the
texture sizes are computed correct. Also the on error
the yet missing inputs to the size computation are
printed which helped me to find out where it really breaks.
Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>