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Re: USB devices non-functional when chainloading Windows 7 from GRUB

From: Will Thompson
Subject: Re: USB devices non-functional when chainloading Windows 7 from GRUB
Date: Mon, 16 Jan 2017 13:47:25 +0000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.6.0

On 14/01/17 08:03, Andrei Borzenkov wrote:
Not really. GRUB does not touch USB at all unless explicitly told to do
so by switching to native drivers or attempting to use USB
keyboard/mouse. It is possible that BIOS puts USB in some state that
*does* require payload to do something.

Does "attempting to use USB keyboard" include invoking "keystatus"? We don't explicitly load "usb" or "usb_keyboard" so my assumption is that this is going through i386/pc/console rather than usb_keyboard, but perhaps I'm wrong?

There were discussions regarding USB handoff for xHCI. As you have USB3
this may be related. Let me look ... OK, subjects are

EHCI handoff & AMI BIOS EHCI Handoff support.​
[PATCH]: xHCI/EHCI - Windows - BIOS bug interaction

and more recent

xHCI driver

although the second one deals with opposite situation - keyboard does
not work in GRUB after reboot from Windows.

Thanks, these are some useful pointers. I don't have physical access to the affected machine so we are at the mercy of the user when it comes to trying possible workarounds. I'll report back if we find anything actionable, and/or whether the user can shed any light on the exact combination of devices and BIOS settings which lead to this situation.

– Will

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