[linux-block.git] / Documentation / arch / x86 / usb-legacy-support.rst


.. SPDX-License-Identifier: GPL-2.0

==================
USB Legacy support
==================

:Author: 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.
Commit	Line	Data
71892b25 CD	1
	2	.. SPDX-License-Identifier: GPL-2.0
	3
	4	==================
1da177e4	5	USB Legacy support
71892b25	6	==================
1da177e4	7
71892b25	8	:Author: Vojtech Pavlik <vojtech@suse.cz>, January 2004
1da177e4 LT	9
	10
	11	Also known as "USB Keyboard" or "USB Mouse support" in the BIOS Setup is a
	12	feature that allows one to use the USB mouse and keyboard as if they were
	13	their classic PS/2 counterparts. This means one can use an USB keyboard to
	14	type in LILO for example.
	15
	16	It has several drawbacks, though:
	17
	18	1) 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
	23	2) If CONFIG_HIGHMEM64G is enabled, the PS/2 mouse emulation can cause
	24	system crashes, because the SMM BIOS is not expecting to be in PAE mode.
	25	The Intel E7505 is a typical machine where this happens.
	26
	27	3) If AMD64 64-bit mode is enabled, again system crashes often happen,
	28	because the SMM BIOS isn't expecting the CPU to be in 64-bit mode. The
	29	BIOS manufacturers only test with Windows, and Windows doesn't do 64-bit
	30	yet.
	31
	32	Solutions:
	33
71892b25 CD	34	Problem 1)
	35	can be solved by loading the USB drivers prior to loading the
	36	PS/2 mouse driver. Since the PS/2 mouse driver is in 2.6 compiled into
	37	the kernel unconditionally, this means the USB drivers need to be
	38	compiled-in, too.
	39
	40	Problem 2)
	41	can currently only be solved by either disabling HIGHMEM64G
	42	in the kernel config or USB Legacy support in the BIOS. A BIOS update
	43	could help, but so far no such update exists.
	44
	45	Problem 3)
	46	is usually fixed by a BIOS update. Check the board
	47	manufacturers web site. If an update is not available, disable USB
	48	Legacy support in the BIOS. If this alone doesn't help, try also adding
	49	idle=poll on the kernel command line. The BIOS may be entering the SMM
	50	on the HLT instruction as well.