Re: [PATCH] usb: core: devio: add ioctls for suspend and resume

[Alan Stern <stern@rowland.harvard.edu>]

On Thu, 27 Jun 2019, Mayuresh Kulkarni wrote:

> Thanks for all the comments and clarifications, Alan.
> 
> I will check the 3-ioctl approach on the platform I have using the test
> program I had used to send my original patch.
> 
> Just for my understanding, the below sequence should also work -
> 1. Call ALLOW_SUSPEND
> 2. Previously queued URB fails ==> device no longer active
> 3. Call WAIT_FOR_RESUME

You don't have to perform (2) if you don't want to.  You can proceed
directly to (3); the WAIT_FOR_RESUME ioctl won't return until the
device has both suspended and resumed (or the call is interrupted by a
signal -- such as a 10-second timer expiring).

> 4. After a while (say > 10 sec), assume no remote-wake by device. But
> user-space wants to communicate with the device (due to some end-user
> activity).
> In this case, the user space needs to call FORBID_SUSPEND ioctl. When
> that returns, it is safe to assume device is active.

Or maybe the WAIT_FOR_RESUME ioctl returns because there was a remote 
wakeup.  In this case also you would call FORBID_SUSPEND.

In fact, you should call FORBID_SUSPEND _whenever_ WAIT_FOR_RESUME
returns, unless your program has decided not to use the device any more
(in which case you don't care whether the device is suspended or
resumed).

> 5. Once done, go-to (1).
> 
> Could you please cross-confirm? Thanks,

That's all correct.

Alan Stern