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/Documentation/i386/usb-legacy-support.txt

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 1USB Legacy support
 2~~~~~~~~~~~~~~~~~~
 3
 4Vojtech Pavlik <vojtech@suse.cz>, January 2004
 5
 6
 7Also known as "USB Keyboard" or "USB Mouse support" in the BIOS Setup is a
 8feature that allows one to use the USB mouse and keyboard as if they were
 9their classic PS/2 counterparts.  This means one can use an USB keyboard to
10type in LILO for example.
11
12It has several drawbacks, though:
13
141) On some machines, the emulated PS/2 mouse takes over even when no USB
15   mouse is present and a real PS/2 mouse is present.  In that case the extra
16   features (wheel, extra buttons, touchpad mode) of the real PS/2 mouse may
17   not be available.
18
192) If CONFIG_HIGHMEM64G is enabled, the PS/2 mouse emulation can cause
20   system crashes, because the SMM BIOS is not expecting to be in PAE mode.
21   The Intel E7505 is a typical machine where this happens.
22
233) 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) can be solved by loading the USB drivers prior to loading the
31PS/2 mouse driver. Since the PS/2 mouse driver is in 2.6 compiled into
32the kernel unconditionally, this means the USB drivers need to be
33compiled-in, too.
34
35Problem 2) can currently only be solved by either disabling HIGHMEM64G
36in the kernel config or USB Legacy support in the BIOS. A BIOS update
37could help, but so far no such update exists.
38
39Problem 3) is usually fixed by a BIOS update. Check the board
40manufacturers web site. If an update is not available, disable USB
41Legacy support in the BIOS. If this alone doesn't help, try also adding
42idle=poll on the kernel command line. The BIOS may be entering the SMM
43on the HLT instruction as well.
44