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authorH. Peter Anvin <hpa@zytor.com>2008-07-22 15:32:38 -0400
committerH. Peter Anvin <hpa@zytor.com>2008-07-22 15:34:38 -0400
commit5616c23ad9cd3c50af674d408fef7b90abeee81c (patch)
tree07409cc0667210336ea071c24a765b0cc1738d84 /Documentation/x86/i386/usb-legacy-support.txt
parent93ded9b8fd42abe2c3607097963d8de6ad9117eb (diff)
x86: doc: move x86-generic documentation from Doc/x86/i386
The boot protocol, USB legacy support, and zero-page documentation is common to the x86 platform, not i386-specific. Signed-off-by: H. Peter Anvin <hpa@zytor.com>
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-USB Legacy support
-~~~~~~~~~~~~~~~~~~
-
-Vojtech Pavlik <vojtech@suse.cz>, 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
- yet.
-
-Solutions:
-
-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
-compiled-in, too.
-
-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.
-