This is about the i2c GPIO chips found in the Sun Fire v210, starting at
/pci/isa@7/i2c@0,320/gpio@0,44
Input/Output assignments and levels are what the firmware leaves us with -
all LEDs off except the power one.

All known pin functions were determined by experiment. No idea what the
undocumented pins do, if anything.

[     1.000000] pcagpio0 at iic0 addr 0x22: PCA9555
[     1.000000] dir: I-IIIIIIIIIIIIII
[     1.000000] lvl: X XXXX  XXX XXXX
[     1.000000] dir: -O--------------
[     1.000000] lvl:  X              
                          ^
0x0400 clears when the case is open

[     1.000000] pcagpio1 at iic0 addr 0x23: PCA9555
[     1.000000] dir: ------IIIIIIIIII
[     1.000000] lvl:       XXXXXXXX  
[     1.000000] dir: OOOOOO----------
[     1.000000] lvl: XXXXXX          
Bit 0x0002 gets set when bay 1 is empty, I would assume 0x0001 is for bay 0.
The output bits seem to control the drive bay LEDs
0x2000 - bay 1, blue LED
0x1000 - bay 0, blue LED
0x0800 - bay 1, both LEDs orange
0x0400 - bay 0, both LEDs orange
all low active, the remaining outputs don't seem to do anything.

[     1.000000] pcagpio2 at iic0 addr 0x34: PCA9555
[     1.000000] dir: --II----IIIIIIII
[     1.000000] lvl:   X     XXXXXXXX
[     1.000000] dir: OO--OOOO--------
[     1.000000] lvl: XX  XXXX        
clearing 0x0300 reset the machine
probably controls redundant / hot-swappable power supplies on v240.

[     1.000000] pcagpio3 at iic0 addr 0x38: PCA9556
[     1.000000] dir: ----------------
[     1.000000] lvl:                 
[     1.000000] dir: OOOOOOOOOOOOOOOO
[     1.000000] lvl:         XXX XXXX
This controls the front panel LEDs
0x80 - indicator LED
0x20 - fault LED
0x10 - power LED
all low active, the remaining outputs don't seem to do anything.