On Mon, 22 Oct 2018 10:24:46 -0400 Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > On Mon, 22 Oct 2018, Oliver Neukum wrote: > > > 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. > > Sure, but you still need a runtime-PM put at the start and a runtime-PM > get at the end. In fact, if you separate this into two calls then you > run the risk that the user may never perform the second call, and you > would end up with an unbalanced put. > I am tending to agree towards having a single ioctl call here. It is better to give minimal control to user-space w.r.t. runtime PM. The current proposal of user-space giving an hint to USB-FS/core that - it is not using the device, sounds better. > > > > /* > > > > * 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? > > This is not meant to be a general-purpose channel for notifying > userspace when a device resumes. Such a channel should be defined in > the runtime-PM layer, not in the USB layer. > > This is instead meant to be a special-purpose mechanism for adding a > runtime-suspend/resume interface to usbfs. > Just to be clear here - the worst case wait-time from user-space perspective will be <time-out - 1 HZ> + <time-to-resume>, right? If yes then, timeout argument means "wait at-least timeout sec". > > > > > > > > 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. > > They won't, because such a sequence cannot occur. The ioctl thread > will wake up when the first resume occurs and it will do a runtime-PM > get, thus preventing any further suspends. > > Alan Stern
