On Mon, 2015-09-21 at 16:02 -0400, Alan Stern wrote:
> On Mon, 21 Sep 2015, Dmitry Torokhov wrote:
>
> > > What happens if the "inhibit" control is turned on and the driver puts
> > > the device into runtime suspend, but then an I/O request arrives?
> > >
> > > If the I/O request originated from userspace, it means the
> > > user is violating the terms of the "inhibit" control. Should
> > > the request simply fail?
> >
> > What user? User that inhibited it or user that tried to use the device?
>
> Normally they would be the same. But even if they aren't, someone has
> violated the kernel interface: The first user told the kernel a
> particular device wasn't going to be used, and then the second user
> tried to use it.
If we assume that user space speaks with a uniform voice on that
issue, it can just as well close the device. It seems to me that
declaring a device idle is a privileged operation.
> Of course, this issue doesn't arise for devices that merely report
> external events.
Indeed. We can handle output to suspended devices by waking them.
I don't see why this case is different. We are talking about input
only.
> The runtime-PM "usage" value for these devices is a little tricky to
> calculate. It should be nonzero if there are any open files _and_ the
> device isn't "inhibited". I don't know the best way to represent that
> kind of condition in the runtime PM framework.
Does that make sense in the generic framework at all? I still
think that drivers should cease IO for input in such cases.
That should involve a common callback, but no counter.
Regards
Oliver
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