On Wednesday, 20 of February 2008, Jesse Barnes wrote: > On Wednesday, February 20, 2008 1:13 pm Linus Torvalds wrote: > > On Wed, 20 Feb 2008, Jesse Barnes wrote: > > > The current callback system looks like this (according to Rafael and the > > > last time I looked): > > > ->suspend(PMSG_FREEZE) > > > ->resume() > > > ->suspend(PMSG_SUSPEND) > > > *enter S3 or power off* > > > ->resume() > > > > Yes, it's very messy. > > > > It's messy for a few different reasons: > > > > - the one you hit: a driver actually has a really hard time telling what > > PMSG_SUSPEND really means. In fact the driver can find out in which state to put the device into, depending on the target ACPI state which is known. > > - more importantly, we generally don't want to "suspend/resume" the > > hardware at all around a power-off, because we're going to resume with > > the state at the time of the PMSG_FREEZE, which means that the hardware > > has actually *changed* and been used in between! > > Exactly. > > > So the "->resume" really isn't a resume at all. It's much closer to a > > "->reset". > > Yeah, in the hibernate case this is definitely true. Agreed. > > Of course, the "solution" to this all right now is that we have to reset > > everything even if it *is* a suspend event, so it basically means that STR > > ends up using the much weaker model that snapshot-to-disk uses. > > > > The fundamental problem being that the two really have nothing > > what-so-ever to do with each other. They aren't even similar. Never were. > > > > > And in the long term we could have: > > > ->suspend() > > > *enter S3* > > > ->resume() > > > > Yes, apart from all the complexities (suspend_late/resume_early). So in > > reality it's more than that, but the suspend/resume things are clearly > > nesting, and they have the potential to actually keep state around > > (because we *know* this machine is not going to mess with the devices in > > between). > > Really, in the simple s3 case we still need early/late stuff? Yes, we do. There are devices that need to be suspended with interrupts off. > > IOW, here we actually can have as an option "assume the device is there > > when you return". That is, unless the user pulls out that pendrive while suspended, no? > > > or: > > > ->hibernate() > > > *kexec to another kernel to save image* > > > *power off* > > > ->return_from_hibernate() (or somesuch) > > > > Enough people don't trust kexec that I suspect the right thing simply is > > > > ->freeze() // stop dma, synchronize device state > > *snapshot* > > ->unfreeze(); // resume dma > > *save image* > > [ optionally ->poweroff() ] // do we really care? I'd say no We do, if there are devices that wake us up from S4 and don't wake us up from S5, for example. Plus this f*cking fan in my box that doesn't work after the resume if we don't do ->poweroff() ... > > *power off* > > ->restore() // reset device to the frozen one > > > > which may have four entry-points that can be illogically mapped to the > > suspend/resume ones like we do now, but they really have nothing to do > > with suspending/resuming. Apart from putting devices into the right low power states, that is. > Well, it seems like we'll have to fix drivers in either case, and isn't a > kexec approach fundamentally more sound and simple, design-wise? Rafael > pointed out some problems with properly setting wakeup states, but I think > that could be overcome... Your honor, I would like to register a differing opinion ... > > And notice how while "freeze/restore" kind of pairs like a > > "suspend/resume", it really shouldn't be expected to realistically restore > > the same state at all. The "restore" part is generally much better seen as > > a "reset hardware" than a "resume" thing. That's absolutely correct. > > Because we literally cannot trust *anything* about the state since we froze > > it - we might have booted a different OS in between etc. Very different from > > suspend/resume. > > Yeah, definitely. It has to be much more robust and deal with configuration > changes, etc. (within reason). Agreed. Thanks, Rafael - To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
