reboot not working on linux-2.6.37 for ARMv7

[Russell King - ARM Linux]

On Fri, Feb 11, 2011 at 05:40:46PM +0530, Santosh Shilimkar wrote:
> > -----Original Message-----
> > From: linux-arm-kernel-bounces at lists.infradead.org [mailto:linux-
> > arm-kernel-bounces at lists.infradead.org] On Behalf Of Russell King -
> > ARM Linux
> > Sent: Friday, February 11, 2011 5:33 PM
> > To: shiraz hashim
> > Cc: Armando VISCONTI; amit.goel at st.com; vipin.kumar at st.com; linux-
> > arm-kernel at lists.infradead.org
> > Subject: Re: reboot not working on linux-2.6.37 for ARMv7
> >
> > On Fri, Feb 11, 2011 at 05:01:06PM +0530, shiraz hashim wrote:
> > > Hi,
> > >
> > > I am using linux-2.6.37 on our ARM Cortex A9 (dual core) SMP
> > platform
> > > with PL310 as Level 2 cache. We observe that on reboot the control
> > > is not able to reach to the arch_reset.
> > >
> > > The problem happens when L1 cache is disabled in
> > > arm_machine_restart, through cpu_proc_fin() and L2 cache is
> > flushed.
> >
> > Where's the L2 cache flush?  The sequence is:
> >
> >         /* Clean and invalidate caches */
> >         flush_cache_all();
> >         /* Turn off caching */
> >         cpu_proc_fin();
> >         /* Push out any further dirty data, and ensure cache is
> > empty */
> >         flush_cache_all();
> >
> > and flush_cache_all() calls v7_flush_kern_cache_all() in
> > arch/arm/mm/cache-v7.S.
> >
> > I do hope you're not modifying flush_cache_all() to also call the L2
> > cache functions because that's wrong.
> >
> I don't want to hijack this thread. But don't we need L2 flush too in
> reboot path ? If the arch_reset function fails because of the data has
> not made it main memory and stuck in L2 which is used as part of this
> function. With C bit disabled, there won't be any look up done in L2.

We only actually need the flushes if we're going to do a soft-reboot.
Soft-reboot isn't supported on ARMv6 and ARMv7 (as the proc-*.S reset
doesn't contain the necessary code).  ARMv5 and lower don't have L2
caches, so its not a concern for them.

Hard-reboot doesn't actually need the cache flushes.  Unfortunately,
we've no way of knowing whether a platform implements soft-reboot or
hard-reboot.