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Re: [Qemu-devel] Disable PS/2 mouse


From: Paul Brook
Subject: Re: [Qemu-devel] Disable PS/2 mouse
Date: Thu, 10 Jun 2010 13:15:31 +0100
User-agent: KMail/1.13.3 (Linux/2.6.33-2-amd64; KDE/4.4.4; x86_64; ; )

> For usb hid devices:  No idea how they work and whenever we can put them
> into sleep somehow (with/without guest cooperation).

The issue with USB is that it is (by design) a polled system. The UHCI adapter 
has to wakeup every 1ms to read transfer descriptors from guest RAM.
Until recently there was a bug in the UHCI emulation that would wake the guest 
even if the tablet NACKed the poll.

See http://lists.nongnu.org/archive/html/qemu-devel/2010-04/msg00150.html


USB does support "autosuspend". This allows a guest to put a device to sleep, 
and have it wake up when something interesting happens.  In theory this 
includes HID devices. However I believe linux disables it because there's so 
much broken hardware out there that implements it incorrectly.  I suspect qemu 
does not currently implement this feature either.

Paul



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