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71892b25 CD |
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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. |