PS2 Support

Controller Type	Game	PS2 Support
Gamepad	Any	Requires nightly build of OPL
Guitar Hero Guitar	Guitar Hero 2	Requires nightly build of OPL
Guitar Hero Guitar	Guitar Hero 3	Requires nightly build of OPL
Guitar Hero Guitar / Guitar Hero Drums	Guitar Hero WT or newer	Works natively
Rock Band Guitar / Rock Band Drums	Rock Band (All Games)	Works natively
DJ Hero Turntable	DJ Hero	Works natively

PS2 controller support is totally dependant on the game and controller type. For games that expect standard gamepad input, you will need to use PADEMU to emulate a standard controller, as the PS2 did not support USB controllers. For Rock Band games, the PS2 used USB instruments, so a controller in Rock Band Guitar or Drum mode will just work.

Guitar Hero games are a bit more complicated. The first two games used a guitar that was based on the Dualshock 1, which used the standard PS2 controller port. For this reason, these games don't support USB instruments. PADEMU will automatically detect PS3 guitars and emulate PS2 Guitars for these games if it is enabled. Guitar Hero World Tour introduced compatibility with PS3 instruments and thus for GHWT or newer, you can just use USB instruments without needing something like PADEMU.

PADEMU

If a PS2 game is expecting a standard controller you usually would not be able to use a USB controller. However, OpenPS2Loader comes with PADEMU, which lets you emulate a PS2 gamepad from a usb device. The firmware is designed to go into PS3 mode when it detects it is plugged into a PS2, and PADEMU has support for both PS3 gamepads and PS3 guitars. Note that for guitars, you need to use a development relase of OPL, as I added support for guitar emulation myself as it originally was not part of PADEMU.