Re: [PATCH 4/4] USB: export autosuspend delay in sysfs

On Fri, 23 Feb 2007, Greg KH wrote:

> > The gist of it runs like this: The autosuspend attribute file controls
> > when & whether autosuspend events will occur.  If you set it to 0 then
> > there will be no more autosuspend events.  Devices that are awake will
> > remain awake and devices that are asleep will remain asleep.  Or to put it
> > another way, lack of any more autosuspend events != presence of an
> > autoresume event.
> 
> Sure, but as the default is 2 seconds, it's hard to change that by hand.

Ah, but the default is now a module parameter, so you can set it in
advance to something larger than 2 seconds!  :-)

> And, if you realize that the device was disabled, you can't turn it back
> on after the fact.
> 
> > Besides, people already do have several ways of turning power back on to a 
> > device.  If you are the superuser you can do
> > 
> > 	echo -n 0 >/sys/bus/usb/devices/.../power/state
> 
> yeah, that file isn't even in my builds anymore :(

Part of the development I did with Oliver was to add a .../power/suspended 
attribute for USB devices.  Writing 1 would immediately suspend the device 
and writing 0 would immediately resume it.  Should I submit that part as a 
separate new patch?

> > (although this is deprecated and will vanish in July -- we may want to add
> > a new attribute file just for USB devices so that people won't lose the
> > ability to do selective suspends and resumes).  Even if you are just a
> > normal user, opening a device's usbfs file will resume that device.  And
> > running any program based on libusb -- such as lsusb -- will wake up all
> > suspended USB devices.
> 
> Oh, that's a fun hack, yeah, that worked...  But try to document that
> one in a simple way.
> 
> I still think that once we write to the autosuspend file, the timer
> should start over, with power enabled.  If this means turning it back
> on, we should.  Otherwise, it's very confusing.

Okay, I'll change it.  Stay tuned...

Alan Stern


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