MX28 poweroff issue

[Russell King - ARM Linux]

On Fri, Jul 06, 2012 at 12:08:58AM +0800, Shawn Guo wrote:
> On Wed, Jul 04, 2012 at 04:19:44PM +0100, Russell King - ARM Linux wrote:
> > If it's specific to mx28 and mx23 and nothing else, the cause needs to
> > be found.  Maybe we need it tested on other (non-MX) platforms too?
> 
> Though people reported that imx27 does not have the problem, I'm not
> so sure about it's a mach-mxs (mx23 and mx28) specific issue.  I have
> not figured it out why imx27 does not run into it, but I got some
> finding here.
> 
> Let's look at the dump again.
> 
> [   59.840000] System halted.
> [   84.100000] BUG: soft lockup - CPU#0 stuck for 23s! [halt:584]
> ...
> [   84.100000] [<c0070cd4>] (watchdog_timer_fn+0x114/0x14c) from [<c004052c>]
> (__run_hrtimer+0x7c/0x1ec)
> 
> It reports the issue eventually in function watchdog_timer_fn
> (kernel/watchdog.c):

Yes, the general idea is that if the timer is running, and the watchdog
is running, and it detects that it's event thread doesn't occasionally
run, it will report a lockup.

As other platforms seem to not exhibit the problem when we halt, and
endlessly spin with IRQs enabled, the question needs to be asked: what
is different with MX23/MX28 and why is it different.

Yes, we can mask the problem by disabling interrupts - just like x86
does - but that doesn't tell us why we have this apparant difference
in behaviours.  I think we need to understand that before we start
heading down the path of disabling interrupts to get rid of this
problem.

So, I think we need some analysis of what's going on here with platforms
that do _not_ exhibit the problem.  Eg, does the timer tick get shut
down?  Does NO_HZ have a bearing on it?  What about timer mode (periodic
vs one shot?)