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This converts the plain text documentation to reStructuredText format and add it to Sphinx TOC tree. No essential content change. Signed-off-by: Changbin Du <changbin.du@gmail.com> Reviewed-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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51 lines
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.. SPDX-License-Identifier: GPL-2.0
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==================
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USB Legacy support
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==================
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:Author: Vojtech Pavlik <vojtech@suse.cz>, January 2004
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Also known as "USB Keyboard" or "USB Mouse support" in the BIOS Setup is a
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feature that allows one to use the USB mouse and keyboard as if they were
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their classic PS/2 counterparts. This means one can use an USB keyboard to
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type in LILO for example.
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It has several drawbacks, though:
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1) On some machines, the emulated PS/2 mouse takes over even when no USB
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mouse is present and a real PS/2 mouse is present. In that case the extra
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features (wheel, extra buttons, touchpad mode) of the real PS/2 mouse may
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not be available.
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2) If CONFIG_HIGHMEM64G is enabled, the PS/2 mouse emulation can cause
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system crashes, because the SMM BIOS is not expecting to be in PAE mode.
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The Intel E7505 is a typical machine where this happens.
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3) If AMD64 64-bit mode is enabled, again system crashes often happen,
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because the SMM BIOS isn't expecting the CPU to be in 64-bit mode. The
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BIOS manufacturers only test with Windows, and Windows doesn't do 64-bit
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yet.
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Solutions:
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Problem 1)
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can be solved by loading the USB drivers prior to loading the
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PS/2 mouse driver. Since the PS/2 mouse driver is in 2.6 compiled into
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the kernel unconditionally, this means the USB drivers need to be
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compiled-in, too.
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Problem 2)
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can currently only be solved by either disabling HIGHMEM64G
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in the kernel config or USB Legacy support in the BIOS. A BIOS update
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could help, but so far no such update exists.
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Problem 3)
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is usually fixed by a BIOS update. Check the board
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manufacturers web site. If an update is not available, disable USB
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Legacy support in the BIOS. If this alone doesn't help, try also adding
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idle=poll on the kernel command line. The BIOS may be entering the SMM
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on the HLT instruction as well.
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