On Wed, 4 Jul 2007, Paul Mackerras wrote: > Alan Stern writes: > > > > Most drivers suspended their hardware in the second call. If they are > > > in the middle of a conversation with their device that *has* to be > > > completed, they can do that by polling. > > > > Ugh. That will cause problems when you try to integrate runtime > > suspend. In fact this whole approach is unsuitable for runtime PM and > > it obscures the similarities between runtime PM and STR. > > Yes there are similarities, but it would be a big mistake to say that > a requirement for STR is that all drivers do runtime PM. That's not what I'm saying. What I'm saying is that it would be a big mistake to force all drivers which implement runtime PM to do it using a separate code path from system PM. > The main attraction of the late-suspend call is that it really does, > reliably, guarantee that the driver's I/O request methods won't get > called between the late-suspend call and the early-resume call. For some drivers (like USB), carrying out an actual suspend requires a delay. Right now we implement those delays using wait_event(), wait_for_completion(), and so on. Would you have us check at runtime whether or not a system suspend is underway and in each case use a busy-loop instead if it is? What happens if, in order to carry out the late-suspend, a driver needs to acquire a mutex which happens to be held by some other task? That other task won't be able to run and release the mutex, so you will deadlock. Alan Stern _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
