[linux-usb-devel] [PATCH] USB: Only enable autosuspend by?default on certain device classes

[linux-usb-devel] [PATCH] USB: Only enable autosuspend by?default on certain device classes

Post by Dave Jone » Sun, 05 Aug 2007 00:00:20



> Am Freitag 03 August 2007 schrieb Dave Jones:

> >
> > > Kernel developers are a diverser lot than you think ;-)
> > > We don't enable autosuspend in drivers we can't test, except where
> > > the lack of a kernel driver forces us to use a broad swipe. Printers
> > > were tested, too, and most printers seem to work.
> >
> > My experience suggests the opposite. Of the several I've tried so far,
> > none have worked with usb suspend.
>
> vendor:product please.

Here's one that I have handy..
Bus 002 Device 004: ID 04a9:1097 Canon, Inc.

(The others aren't powered on right now, and I'm remote from them ;-)

Dave

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The correct answer is that HAL should top polling while the device is
suspended.

In kernels starting with 2.6.23-rc6, the correct way to enable
autosuspend for a USB device is basically like this:

echo D >/sys/bus/usb/devices/.../power/autosuspend
echo auto >/sys/bus/usb/devices/.../power/level

where D is the time (in seconds) the device should remain idle before
it is autosuspended. An autosuspended device will be woken up to
respond to polls. (Note however that in this kernel, autosuspend
support for USB mass-storage devices was removed because it can
cause problems related to spinning down disk drives.)

If instead you do

echo suspend >/sys/bus/usb/devices/.../power/level

it will simply suspend the device immediately. The device will not be
woken up automatically and attempts to poll it (or do anything else)
will fail.

Alan Stern

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