Neo Freerunner PMU Status

[Harald Welte]

On Fri, Feb 08, 2008 at 03:46:16PM +0000, Andy Green wrote:
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> Somebody in the thread at some point said:
> > On Fri, Feb 08, 2008 at 11:36:38AM +0000, Andy Green wrote:
> > 
> >> Ha -- looks like the PCF50633 "LOWBAT" interrupt service tries always to
> >> do kill_proc(1, SIGPWR, 1); when LOWBAT really means *NO*BAT -- it kills
> >> the garbage collection fork stone dead when it tries to start instead
> >> and finds that signal waiting there.  I guess the GTA01 PMU driver did
> >> the same...
> > 
> > Yes.  This is the desired behaviour.  Traditionally, unix power failures
> > are signalled to the init process by means of SIGPWR.  Even 20-30 year
> > old code can deal with that :)
> 
> It's really the desired behaviour that if we don't have a battery in
> this device it tries to kill init?  I don't think I desire it -- I want
> the device to stay up without a battery so long as I give it power
> another way (patches coming).

no, you misunderstood me.  your fix to not send SIGPWR in case there
actually is power provided via USB is obviously correct.

However, this SIGPWR-to-garbage-collector can still happen, in the
actual case of low battery voltage and no power being supplied via USB.

So you're just making the problem appear less frequently, but the
problem should still persist, right?

> > Now the question is rather: why is that garbage collection thread using
> > PID 1.  It shouldn't do that, since that PID is reserved for init and
> > nothing else.
> > 
> > It's probably worth pushing this question to linux-mtd and/or dwmw2
> > directly.
> 
> This issue belongs to nobody less than Linus I think -- I saw he wrote
> the fork.c code that associates the signal with the kernel thread for
> the garbage collection.  I think the issue is more correctly that the
> process does not appear in the process table yet at the time it blows
> chunks, therefore I guess it doesn't have ANY process ID.  Somehow it is
> affected by pending signals to nonexistant pids.

;) well.  Sending it to Linus is probably a bit of an exaggeration. but
lkml is fine, certainly.

-- 
- Harald Welte <laforge at openmoko.org>          	        http://openmoko.org/
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