Re: [Zaurus-devel] [suspend/resume] Re: userspace notification from module
On Sun, Jan 17, 2010 at 02:07:39PM +0100, Pavel Machek wrote: AFAICT following message would be nice. 1) battery is critical, userspace please do something On zaurus and similar, you could add 2) oh and btw we had power failure so we suspended (or maybe -- so hardware suspended itself -- rmk's examples and old apm systems); we are now back and running notification... but... ideally those power failures should never happen anyway, so... having this notification is in no way neccessary. There's another consideration here: the more complex the emergency procedure, the higher the chance of _something_ causing it to fail, and if it does fail, the result is data loss. In a properly running system, this isn't something that's going to get a lot of testing, so there's a higher chance that there will be bugs, so the simpler the solution, the better. It's a bit like the kernel shutdown paths - because they don't get a lot of use, they don't get tested enough, and having discussed it with Arjan van de Ven, it's a known weakness. So we know that they're not that well tested - and the result is eg, 33-rc3 on shutdown results in an oops for me on x86. You really don't want to oops or deadlock on battery critically low. ___ Zaurus-devel mailing list Zaurus-devel@lists.linuxtogo.org http://lists.linuxtogo.org/cgi-bin/mailman/listinfo/zaurus-devel
Re: [Zaurus-devel] [suspend/resume] Re: userspace notification from module
Hi! I wasn't aware of this. That may be a good reason for adding kernel-based suspend notification, although I'd prefer ARM to notify the user space about the critical battery status allowing it to decide what to do. Hard to do, without breaking compatibility that goes down to 2.4.X. Sending a battery-critical notification to the user space is not equivalent to removing the existing kernel-based mechanism. They can exist both at the same time if the notification is sent earlier than the kernel suspends everything. Yes, and obviously sending notification early is ok with me. It really makes sense on zaurus. Those machines are simple, no smartbattery and no embedded controller subsystems. Battery will not protect itself, and its kernel job. (Should work on init=/bin/bash). As power-off consumption is same as suspend power consumption (I beleive zaurus simply does not have true power off), suspend on critical makes some sense. (Note that it is set lower than on pcs, and that we declare battery critical sooner than that.) The problem with that is it catches at least some applications unprepared and notifying them that we're suspending right now doesn't really help, because they won't have any time to react anyway. Agreed, but so what? On PC, machine would power off at that point. That would surprise the apps, too. Basically new enough userland should not make battery run low enough for either emergency power off or emergency suspend. IOW nothing to see here, problem does not exist. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html ___ Zaurus-devel mailing list Zaurus-devel@lists.linuxtogo.org http://lists.linuxtogo.org/cgi-bin/mailman/listinfo/zaurus-devel
Re: [Zaurus-devel] [suspend/resume] Re: userspace notification from module
On Sat 2010-01-16 18:00:58, Stanislav Brabec wrote: Eric Miao wrote: And the other way we may need to look into what API the current userland apps on zaurus is depending on this 2.4 compatibility and make changes slowly to those apps. I guess that 2.4 compatibility is not an issue. Most modern Zaurus distributions are even unable to run Sharp ROM compatible binaries. Distributions either stay on 2.4 kernel or use modern systems based on modern kernel 2.6 API. Distributions that decided to migrate to kernel 2.6 are far from finished state. Any change that allows to use modern applications using standard kernel API is welcome. There is no API involved. It is just ... if you leave zaurus in init=/bin/bash mode, it must not kill the battery. Smart and currently implemented way to do that is to suspend. That's counterexample to rjw, but it does not matter -- reasonable userland should never ever hit that, in a same way PCs should not hit emergency power cut... Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html ___ Zaurus-devel mailing list Zaurus-devel@lists.linuxtogo.org http://lists.linuxtogo.org/cgi-bin/mailman/listinfo/zaurus-devel
Re: [Zaurus-devel] [suspend/resume] Re: userspace notification from module
On Saturday 16 January 2010, Pavel Machek wrote: On Sat 2010-01-16 18:00:58, Stanislav Brabec wrote: Eric Miao wrote: And the other way we may need to look into what API the current userland apps on zaurus is depending on this 2.4 compatibility and make changes slowly to those apps. I guess that 2.4 compatibility is not an issue. Most modern Zaurus distributions are even unable to run Sharp ROM compatible binaries. Distributions either stay on 2.4 kernel or use modern systems based on modern kernel 2.6 API. Distributions that decided to migrate to kernel 2.6 are far from finished state. Any change that allows to use modern applications using standard kernel API is welcome. There is no API involved. It is just ... if you leave zaurus in init=/bin/bash mode, it must not kill the battery. Smart and currently implemented way to do that is to suspend. IMHO it should just plain shutdown in that case. Suspending doesn't really solve the problem, because the battery is going to drain still. Unless you mean suspend=hibernate, but I guess you don't. That's counterexample to rjw, but it does not matter -- reasonable userland should never ever hit that, in a same way PCs should not hit emergency power cut... I don't really understand what you mean. The user space doesn't know the battery state if the kernel doesn't tell it, AFAICS, so how exactly can it predict the critical battery condition without the kernel notifying it? Rafael ___ Zaurus-devel mailing list Zaurus-devel@lists.linuxtogo.org http://lists.linuxtogo.org/cgi-bin/mailman/listinfo/zaurus-devel
Re: [Zaurus-devel] [suspend/resume] Re: userspace notification from module
On Saturday 16 January 2010, Pavel Machek wrote: Hi! Agreed, but so what? On PC, machine would power off at that point. That would surprise the apps, too. Basically new enough userland should not make battery run low enough for either emergency power off or emergency suspend. I wonder how it is supposed to achieve that without knowing the current battery status. Do you mean it should poll the battery driver? That's besides point, is it? Well, mentioned that first. :-) Usual kernel-user interfaces should apply here. And we're talking about the design of these, aren't we? The notification about the critical battery status sent to the user space is a part of the kernel-user space interface too, after all. Rafael ___ Zaurus-devel mailing list Zaurus-devel@lists.linuxtogo.org http://lists.linuxtogo.org/cgi-bin/mailman/listinfo/zaurus-devel
