On Tue, 27 Jun 2006, Benjamin Herrenschmidt wrote: > > I'm not sure actually _why_ we should have irqs off if we do the job > properly If we were able to do the job properly, I'd agree. I just claim that the last few years have shown that we aren't. I want that last suspend_late/resume_early to be done with interrupts disabled exactly because most of the problems I've seen in suspend/resume have been due to things like some subsystem calling into a driver that was partially shut down, or a shared interrupt happening for a driver that can't take it any more etc etc etc. So for me, the absolutely _humongous_ advantage to doing the last (and the very first) phase with irq's off and in single-CPU mode is exactly that people _do_ get it wrong. So I'd much rather have a more limited mode that allows people to basically think of suspend as something very controlled where nothing else happens, and they can _depend_ on that. And the thing is, if you want to write a perfect driver, you still have that _option_. You don't have to use the late/early suspend if you don't want to, as a driver writer. I absolutely hate complexity and "perfect". I'd _much_ rather see the model be that you're in this really really limited mode when you do the final suspend, and have people do bit-twiddling and busy-waits. It may sound inconvenient, but the thing is, from a driver writer perspective, I think enforcing limitations is actually _good_. For example, I hate ACPI and EFI with a passion. I actually think that the old stupif BIOS is infinitely more preferable as a loader, exactly because it's _so_ stupid that people don't try to do something clever in it, and don't try to use it. But because of that stupidity it _works_. Suspend/resume shouldn't need to be "good". It doesn't need multi-processing, and the final (and most fragile phases) of turning off the core components of the montherboard doesn't need interrupts. What if the interrupt controller or timers or whatever aren't strictly a "parent" of the devices that need it? THAT'S OK. (It's also more than OK - it's a fact of life on some things. It should be ok to shut off the interrupt controller before you shut off some devices, and it should be ok to bring core devices up before the interrupt controller is even working). So all of this means that I don't think the system should be "live" during the last phase. It should be as dead as humanly possible. Linus
