Re: [PATCH v2] clocksource: arm_global_timer: fix suspend resume

[santosh shilimkar]

On 11/20/2015 10:46 AM, Marc Zyngier wrote:
> On 20/11/15 18:35, Grygorii Strashko wrote:
> > Hi Santosh,
> >
> > On 11/20/2015 07:23 PM, santosh shilimkar wrote:
> > > + Thomas, Marc
> > >
> > > On 11/20/2015 5:57 AM, Grygorii Strashko wrote:
> > > > Now the System stall is observed on TI AM437x based board
> > > > (am437x-gp-evm) during resuming from System suspend when ARM Global
> > > > timer is selected as clocksource device - SysRq are working, but
> > > > nothing else. The reason of stall is that ARM Global timer loses its
> > > > contexts.
> > > >
> > > > The reason of stall is that ARM Global timer loses its contexts during
> > > > System suspend:
> > > >      GT_CONTROL.TIMER_ENABLE = 0 (unbanked)
> > > >      GT_COUNTERx = 0
> > > >
> > > > Hence, update ARM Global timer driver to reflect above behaviour
> > > > - re-enable ARM Global timer on resume GT_CONTROL.TIMER_ENABLE = 1
> > > > - ensure clocksource and clockevent devices have coresponding flags
> > > >     (CLOCK_SOURCE_SUSPEND_NONSTOP and CLOCK_EVT_FEAT_C3STOP) set
> > > >     depending on presence of "always-on" DT property.
> > > Something which loses context in low power states can't be
> > > called "always-on"
> >
> > Sry, it's kinda new area for me and I could make mistakes.
> >
> > While working on this patch I've:
> >   - re-used implementation from ARM arch timer
> > commit 82a5619410d4c4df65c04272db198eca5a867c18
> > Author: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx>
> > Date:   Tue Apr 8 10:04:32 2014 +0100
> >
> >      clocksource: arch_arm_timer: Fix age-old arch timer C3STOP detection issue
>
> [...]
>
> This patch has a very specific purpose: instructing the core code that
> this timer will never stop ticking, ever. It is really targeted at
> virtual machines, whose timer is backed by the host timer, even when the
> VM is not running.
>
> Using it on actual hardware is may not be the best idea, specially in
> the presence of PM.
Exactly. Thanks for clarifying the commit Marc.

Regards,
Santosh
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