We just need to clear the SBA and ENABLE bits to reset the AGP
controller: If the AGP bridge was configured to use "fast writes",
clearing the FW bit would break the subsequent MMIO writes and
eventually end with a lockup.
Note that all the BIOSes I've seen do the same as we did (it works for
them because they don't use MMIO), OTOH the blob leaves FW untouched.
Signed-off-by: Francisco Jerez <currojerez@riseup.net>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
190a43783f