|USB Legacy support
|Vojtech Pavlik <firstname.lastname@example.org>, January 2004
|Also known as "USB Keyboard" or "USB Mouse support" in the BIOS Setup is a
|feature that allows one to use the USB mouse and keyboard as if they were
|their classic PS/2 counterparts. This means one can use an USB keyboard to
|type in LILO for example.
|It has several drawbacks, though:
|1) On some machines, the emulated PS/2 mouse takes over even when no USB
| mouse is present and a real PS/2 mouse is present. In that case the extra
| features (wheel, extra buttons, touchpad mode) of the real PS/2 mouse may
| not be available.
|2) If CONFIG_HIGHMEM64G is enabled, the PS/2 mouse emulation can cause
| system crashes, because the SMM BIOS is not expecting to be in PAE mode.
| The Intel E7505 is a typical machine where this happens.
|3) If AMD64 64-bit mode is enabled, again system crashes often happen,
| because the SMM BIOS isn't expecting the CPU to be in 64-bit mode. The
| BIOS manufacturers only test with Windows, and Windows doesn't do 64-bit
|Problem 1) can be solved by loading the USB drivers prior to loading the
|PS/2 mouse driver. Since the PS/2 mouse driver is in 2.6 compiled into
|the kernel unconditionally, this means the USB drivers need to be
|Problem 2) can currently only be solved by either disabling HIGHMEM64G
|in the kernel config or USB Legacy support in the BIOS. A BIOS update
|could help, but so far no such update exists.
|Problem 3) is usually fixed by a BIOS update. Check the board
|manufacturers web site. If an update is not available, disable USB
|Legacy support in the BIOS. If this alone doesn't help, try also adding
|idle=poll on the kernel command line. The BIOS may be entering the SMM
|on the HLT instruction as well.