On Do, 2018-10-18 at 13:42 -0400, Alan Stern wrote: > On Thu, 18 Oct 2018, Mayuresh Kulkarni wrote: > > > > The only way to make the ioctl work properly is to have it do a > > > runtime-PM put at the start and then a runtime-PM get before it If and only if you want to do this with one ioctl() If you separate the runtime-PM put and the get, you can do it without the waiting part. > > > returns. This is true regardless of the reason for returning: normal > > > termination, timeout, signal, whatever. Nothing else would be safe. > > > > > > > Will below steps work safely (sometimes pseudo-code/snippets help to align)? - > > > > "new" ioctl - > > > > timeout is parameter to ioctl. > > > > /* attempt suspend of device */ > > usb_autosuspend_device(dev); > > > > usb_unlock_device(dev); > > r = wait_event_interruptible_timeout(ps->resume_wait, > > (ps->resume_done == true), timeout * HZ); > > Not exactly. The condition to test here is whether the device has been > suspended, so it's more like this: > > r = wait_event_interruptible_timeout(ps->suspend_wait, > (ps->suspend_done == true), timeout * HZ); > > where ps->suspend_done is set by the runtime_suspend callback. After > this we will do: > > if (r > 0) /* Device suspended before the timeout expired */ > r = wait_event_interruptible(ps->resume_wait, > (ps->resume_done == true)); > > > usb_lock_device(dev); > > > > /* > > * There are 3 possibilities here: > > * 1. Device did suspend and resume (success) > > * 2. Signal was received (failed suspend) > > * 3. Time-out happened (failed suspend) > > 4. Device did suspend but a signal was received before the device > resumed. > > > * In any of above cases, we need to resume device. > > */ > > usb_autoresume_device(dev); Yes and that is the problem. Why do you want to wait for the result of runtime-PM put ? If we need a channel for notifying user space about resume of a device, why wait for the result of suspend instead of using the same channel? > > > > ps->resume_done = false; > > > > "ps->resume_done = true;" will be done by the runtime resume call-back. No. You cannot do that in this way. It needs to be a unified device state or a sequence of multiple suspends and resumes will have strange results. Regards Oliver
