1
2.. SPDX-License-Identifier: GPL-2.0
3
4==================
5USB Legacy support
6==================
7
8:Author: Vojtech Pavlik <vojtech@suse.cz>, January 2004
9
10
11Also known as "USB Keyboard" or "USB Mouse support" in the BIOS Setup is a
12feature that allows one to use the USB mouse and keyboard as if they were
13their classic PS/2 counterparts.  This means one can use an USB keyboard to
14type in LILO for example.
15
16It has several drawbacks, though:
17
181) On some machines, the emulated PS/2 mouse takes over even when no USB
19   mouse is present and a real PS/2 mouse is present.  In that case the extra
20   features (wheel, extra buttons, touchpad mode) of the real PS/2 mouse may
21   not be available.
22
232) If AMD64 64-bit mode is enabled, again system crashes often happen,
24   because the SMM BIOS isn't expecting the CPU to be in 64-bit mode.  The
25   BIOS manufacturers only test with Windows, and Windows doesn't do 64-bit
26   yet.
27
28Solutions:
29
30Problem 1)
31  can be solved by loading the USB drivers prior to loading the
32  PS/2 mouse driver. Since the PS/2 mouse driver is in 2.6 compiled into
33  the kernel unconditionally, this means the USB drivers need to be
34  compiled-in, too.
35
36Problem 2)
37  is usually fixed by a BIOS update. Check the board
38  manufacturers web site. If an update is not available, disable USB
39  Legacy support in the BIOS. If this alone doesn't help, try also adding
40  idle=poll on the kernel command line. The BIOS may be entering the SMM
41  on the HLT instruction as well.
42