Don't clobber the GPIO I/O Base value.
According to the PC87307 datasheet, port 0x60 bits [2:7] are read-only
for the Parallel Port (4) device and cannot be altered by software.
For others devices, the 0x60 port may be written with any value.
The SGI firmware emits the following PC87307 initialization sequence
after each reset:
/* Select the GPIO device (7) */
SIO IDX: 2E <-- 07
SIO DAT: 2F <-- 07
/* I/O Base MSB = 0x0F */
SIO IDX: 2E <-- 60
SIO DAT: 2F <-- 0F
/* I/O Base LSB = 0xC0 */
SIO IDX: 2E <-- 61
SIO DAT: 2F <-- C0
/* Enable address decoding (I/O Base = 0xFC0) */
SIO IDX: 2E <-- 30
SIO DAT: 2F <-- 01
The GPIO I/O Base is erroneously assigned to 0x7C0. Fix by removing the 0x07 mask.
8dc0beaeec