Re: [PATCH] udev: add rules for qemu guests

[Gerd Hoffmann <kraxel@redhat.com>]

On 01/25/11 14:39, Kay Sievers wrote:
> On Tue, Jan 25, 2011 at 11:44, Gerd Hoffmann<kraxel@redhat.com>  wrote:
>> These patches enable usb autosuspend for the qemu emulated HID devices.
>> This reduces the cpu load for idle guests with a hid device attached
>> because the linux kernel will suspend the usb bus then and qemu can stop
>> running a 1000 Hz to emulate the (active) UHCI controller.
>
>> +dist_udevrules_DATA += extras/qemu/99-qemu-usb.rules
>
> The number should be 10-90 for the default things, or is there a
> dependency on anything else?

No dependency at all.  What number do you suggest then?

>> +ACTION="add", SUBSYSTEM="usb", ATTR{product}="QEMU USB Mouse", ATTR{serial}="42", RUN+="qemu-usb-autosuspend %p"
>
> This should probably be a simple ATTR{power/control}="auto"

That should work indeed.  Didn't know you can write sysfs files that way.

>> +path="$1"
>> +if test -f "/sys${path}/power/control"; then
>> +       echo "auto">  "/sys${path}/power/control"
>> +elif test -f "/sys${path}/power/level"; then
>> +       echo "auto">  "/sys${path}/power/level"
>> +fi
>
> Which one is the actual one? Is the second try only for older kernels?

Yes, it is for older kernels.

> That could go in the compat rules, udev does not ship rules for older
> kernels in the default installation.

Ok.  Is there some way to express "power/control doesn't exist but 
power/level does" as udev rule, so I can zap the shell script?

> Anyway, why isn't all this done in the kernel? Can't this be made
> working somehow?

As far I know the kernel doesn't do that by default because too much 
broken hardware is out there which breaks when autosuspend is enabled by 
default.  I saw mentioned somewhere the plan is to have udev enable this 
for known-good devices, so I'm trying that route :)

Havn't checked whenever there is a in-kernel white list for that stuff 
which could be used instead.

cheers,
   Gerd