--- On Sun, 6/20/10, David Brownell <david-b@xxxxxxxxxxx> wrote: ... in a sort of "aren't we asking the wrong questions??" manner ... I suspect that looking at the problem in terms of how to coordinate subsystems (an abstraction which is at best very ad-hoc today!) we would end up with a cleaner model, which doesn't bother so many folk the ay wakelocks or even suspend blockers seem to bother them... > From: David Brownell <david-b@xxxxxxxxxxx> > Subject: Re: [RFC][PATCH] PM: Avoid losing wakeup events during suspend > To: markgross@xxxxxxxxxxx, "Alan Stern" <stern@xxxxxxxxxxxxxxxxxxx> > Cc: "Neil Brown" <neilb@xxxxxxx>, linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx, "Dmitry Torokhov" <dmitry.torokhov@xxxxxxxxx>, "Linux Kernel Mailing List" <linux-kernel@xxxxxxxxxxxxxxx>, "mark gross" <640e9920@xxxxxxxxx> > Date: Sunday, June 20, 2010, 9:04 PM > > > > > Indeed, the same problem arises if the > event > > isn't delivered to > > > > userspace until after userspace is frozen. > > Can we put this more directly: the problem is > that the *SYSTEM ISN'T FULLY SUSPENDED* when the > hardware wake event triggers? (Where "*SYSTEM* > includes userspace not just kernel. In fact the > overall system is built from many subsystems, > some in the kernel and some in userspace. > > At the risk of being prematurely general: I'd > point out that these subsystems probably have > sequencing requirements. kernel-then-user is > a degenerate case, and surely oversimplified. > There are other examples, e.g. between kernel > subsystems... Like needing to suspend a PMIC > before the bus it uses, where that bus uses > a task to manage request/response protocols. > (Think I2C or SPI.) > > This is like the __init/__exit sequencing mess... > > In terms of userspace event delivery, I'd say > it's a bug in the event mechanism if taking the > next step in suspension drops any event. It > should be queued, not lost... As a rule the > hardware queuing works (transparently)... > > > Of course, the underlying > > > > issue here is that the kernel has no direct > way > > to know when userspace > > > > has finished processing an event. > > > Again said more directly: there's no current > mechanism to coordinate subsystems. Userspace > can't communicate "I'm ready" to kernel, and > vice versa. (a few decades ago, APM could do > that ... we dropped such mechanisms though, and > I'm fairly sure APM's implementation was holey.) > > > > > _______________________________________________ > linux-pm mailing list > linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx > https://lists.linux-foundation.org/mailman/listinfo/linux-pm > _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
