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1 2.. SPDX-License-Identifier: GPL-2.03 4==================5USB Legacy support6==================7 8:Author: Vojtech Pavlik <vojtech@suse.cz>, January 20049 10 11Also known as "USB Keyboard" or "USB Mouse support" in the BIOS Setup is a12feature that allows one to use the USB mouse and keyboard as if they were13their classic PS/2 counterparts. This means one can use an USB keyboard to14type 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 USB19 mouse is present and a real PS/2 mouse is present. In that case the extra20 features (wheel, extra buttons, touchpad mode) of the real PS/2 mouse may21 not be available.22 232) If CONFIG_HIGHMEM64G is enabled, the PS/2 mouse emulation can cause24 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.26 273) 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. The29 BIOS manufacturers only test with Windows, and Windows doesn't do 64-bit30 yet.31 32Solutions:33 34Problem 1)35 can be solved by loading the USB drivers prior to loading the36 PS/2 mouse driver. Since the PS/2 mouse driver is in 2.6 compiled into37 the kernel unconditionally, this means the USB drivers need to be38 compiled-in, too.39 40Problem 2)41 can currently only be solved by either disabling HIGHMEM64G42 in the kernel config or USB Legacy support in the BIOS. A BIOS update43 could help, but so far no such update exists.44 45Problem 3)46 is usually fixed by a BIOS update. Check the board47 manufacturers web site. If an update is not available, disable USB48 Legacy support in the BIOS. If this alone doesn't help, try also adding49 idle=poll on the kernel command line. The BIOS may be entering the SMM50 on the HLT instruction as well.51