On Mo, 2018-10-15 at 09:50 -0400, Alan Stern wrote:
>
> It seems that a better approach would be to have an ioctl which would:
>
> fail if there are any active user URBs;
>
> drop the usbfs PM reference so the device can suspend;
>
> block interruptibly until the device resumes;
Thus we would require user space to have a thread for each device
it wants to allow suspend for.
[..]
> What difference does it make if the URBs are killed by the user instead
> of the kernel?
We stay within the limits of the timing (as well as we can) and the
case of a failed suspend is much easier to handle.
Else we have an unlimited time between cessation of IO and going
into suspend.
> > And notify user space when the device is resumed. IMHO select()
> > is the syscall designed for that.
>
> Apart from the difficulties mentioned above.
Yes, I see.
Regards
Oliver
