1*4882a593Smuzhiyun 2*4882a593Smuzhiyun.. SPDX-License-Identifier: GPL-2.0 3*4882a593Smuzhiyun 4*4882a593Smuzhiyun================== 5*4882a593SmuzhiyunUSB Legacy support 6*4882a593Smuzhiyun================== 7*4882a593Smuzhiyun 8*4882a593Smuzhiyun:Author: Vojtech Pavlik <vojtech@suse.cz>, January 2004 9*4882a593Smuzhiyun 10*4882a593Smuzhiyun 11*4882a593SmuzhiyunAlso known as "USB Keyboard" or "USB Mouse support" in the BIOS Setup is a 12*4882a593Smuzhiyunfeature that allows one to use the USB mouse and keyboard as if they were 13*4882a593Smuzhiyuntheir classic PS/2 counterparts. This means one can use an USB keyboard to 14*4882a593Smuzhiyuntype in LILO for example. 15*4882a593Smuzhiyun 16*4882a593SmuzhiyunIt has several drawbacks, though: 17*4882a593Smuzhiyun 18*4882a593Smuzhiyun1) On some machines, the emulated PS/2 mouse takes over even when no USB 19*4882a593Smuzhiyun mouse is present and a real PS/2 mouse is present. In that case the extra 20*4882a593Smuzhiyun features (wheel, extra buttons, touchpad mode) of the real PS/2 mouse may 21*4882a593Smuzhiyun not be available. 22*4882a593Smuzhiyun 23*4882a593Smuzhiyun2) If CONFIG_HIGHMEM64G is enabled, the PS/2 mouse emulation can cause 24*4882a593Smuzhiyun system crashes, because the SMM BIOS is not expecting to be in PAE mode. 25*4882a593Smuzhiyun The Intel E7505 is a typical machine where this happens. 26*4882a593Smuzhiyun 27*4882a593Smuzhiyun3) If AMD64 64-bit mode is enabled, again system crashes often happen, 28*4882a593Smuzhiyun because the SMM BIOS isn't expecting the CPU to be in 64-bit mode. The 29*4882a593Smuzhiyun BIOS manufacturers only test with Windows, and Windows doesn't do 64-bit 30*4882a593Smuzhiyun yet. 31*4882a593Smuzhiyun 32*4882a593SmuzhiyunSolutions: 33*4882a593Smuzhiyun 34*4882a593SmuzhiyunProblem 1) 35*4882a593Smuzhiyun can be solved by loading the USB drivers prior to loading the 36*4882a593Smuzhiyun PS/2 mouse driver. Since the PS/2 mouse driver is in 2.6 compiled into 37*4882a593Smuzhiyun the kernel unconditionally, this means the USB drivers need to be 38*4882a593Smuzhiyun compiled-in, too. 39*4882a593Smuzhiyun 40*4882a593SmuzhiyunProblem 2) 41*4882a593Smuzhiyun can currently only be solved by either disabling HIGHMEM64G 42*4882a593Smuzhiyun in the kernel config or USB Legacy support in the BIOS. A BIOS update 43*4882a593Smuzhiyun could help, but so far no such update exists. 44*4882a593Smuzhiyun 45*4882a593SmuzhiyunProblem 3) 46*4882a593Smuzhiyun is usually fixed by a BIOS update. Check the board 47*4882a593Smuzhiyun manufacturers web site. If an update is not available, disable USB 48*4882a593Smuzhiyun Legacy support in the BIOS. If this alone doesn't help, try also adding 49*4882a593Smuzhiyun idle=poll on the kernel command line. The BIOS may be entering the SMM 50*4882a593Smuzhiyun on the HLT instruction as well. 51