Re: defficiencies in the hid autosuspend code

On Thu, 4 Oct 2007, Oliver Neukum wrote:

> Am Donnerstag 04 Oktober 2007 schrieb Alan Stern:
> > I'm not sure I understand your problem.  Are you saying that some 
> > devices will work okay with autosuspend so long as the device file 
> > isn't open, whereas other devices will work okay even when the device 
> > file is open?
> 
> Yes.
> 
> > In that case there are two possible solutions.  One is to rely on 
> > userspace to disable autosuspend whenever it opens the device file.
> > This may not be practical, but in the end something like it may turn 
> > out to be best.
> > 
> > The other is to figure out some way for the driver to know whether the
> > open routine should call usb_autopm_get_interface(), and similarly for
> > the close routine.  I don't like the idea of adding a sysfs attribute
> > for this, or even changing the power/level attribute (e.g., add an 
> > "auto-closed" setting).
> 
> Do you think HID will be the only driver with this problem?
> I doubt it. There'll be cases of devices not allowing aggresive
> power save, but allowing mild measures.

That may well be true.  Do you think those other drivers will be able 
to tell the two kinds of devices apart more easily than usbhid?  If the 
driver can tell what kind of device it's dealing with, there's no 
problem.  And this really isn't the sort of thing the user should have 
to worry about.

Alan Stern


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