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

[Grygorii Strashko]

On 11/13/2015 08:15 PM, Felipe Balbi wrote:
> Hi,
>
> Grygorii Strashko <grygorii.strashko@xxxxxx> writes:
> > On 11/13/2015 07:40 PM, Felipe Balbi wrote:
> > > Hi,
> > >
> > > Grygorii Strashko <grygorii.strashko@xxxxxx> writes:
> > > > On 11/13/2015 06:43 PM, Felipe Balbi wrote:
> > > > > Hi,
> > > > >
> > > > > Grygorii Strashko <grygorii.strashko@xxxxxx> writes:
> > > > > > 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
> > > > > > - save GT_CONTROL.TIMER_ENABLE during suspend and restore on resume;
> > > > > > - 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.
> > > > > >
> > > > > > CC: Arnd Bergmann <arnd@xxxxxxxx>
> > > > > > Cc: John Stultz <john.stultz@xxxxxxxxxx>
> > > > > > Cc: Felipe Balbi <balbi@xxxxxx>
> > > > > > Cc: Tony Lindgren <tony@xxxxxxxxxxx>
> > > > > > Signed-off-by: Grygorii Strashko <grygorii.strashko@xxxxxx>
> > > > > > ---
> > > > > >     drivers/clocksource/arm_global_timer.c | 23 +++++++++++++++++++++++
> > > > > >     1 file changed, 23 insertions(+)
> > > > > >
> > > > > > diff --git a/drivers/clocksource/arm_global_timer.c b/drivers/clocksource/arm_global_timer.c
> > > > > > index a2cb6fa..1bbaf64 100644
> > > > > > --- a/drivers/clocksource/arm_global_timer.c
> > > > > > +++ b/drivers/clocksource/arm_global_timer.c
> > > > > > @@ -51,6 +51,8 @@ static void __iomem *gt_base;
> > > > > >     static unsigned long gt_clk_rate;
> > > > > >     static int gt_ppi;
> > > > > >     static struct clock_event_device __percpu *gt_evt;
> > > > > > +static bool gt_always_on;
> > > > > > +static u32 gt_control;
> > > > > >
> > > > > >     /*
> > > > > >      * To get the value from the Global Timer Counter register proceed as follows:
> > > > > > @@ -168,6 +170,9 @@ static int gt_clockevents_init(struct clock_event_device *clk)
> > > > > >     {
> > > > > >     	int cpu = smp_processor_id();
> > > > > >
> > > > > > +	if (!gt_always_on)
> > > > > > +		clk->features |= CLOCK_EVT_FEAT_C3STOP;
> > > > > > +
> > > > > >     	clk->name = "arm_global_timer";
> > > > > >     	clk->features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT |
> > > > > >     		CLOCK_EVT_FEAT_PERCPU;
> > > > > > @@ -195,12 +200,25 @@ static cycle_t gt_clocksource_read(struct clocksource *cs)
> > > > > >     	return gt_counter_read();
> > > > > >     }
> > > > > >
> > > > > > +static void gt_suspend(struct clocksource *cs)
> > > > > > +{
> > > > > > +	gt_control = readl(gt_base + GT_CONTROL);
> > > > > > +}
> > > > > > +
> > > > > > +static void gt_resume(struct clocksource *cs)
> > > > > > +{
> > > > > > +	/* enables timer on all the cores */
> > > > > > +	writel(gt_control & GT_CONTROL_TIMER_ENABLE, gt_base + GT_CONTROL);
> > > > >
> > > > > do you really need to save context if all you restore is TIMER_ENABLE
> > > > > bit ? seems like you could skip gt_suspend altogether. Is there really a
> > > > > situation where this driver is running and GT isn't enabled ?
> > > >
> > > > Now It's not. It's always enabled. I did it because .suspend() is called for
> > > > all registered clock sources regardless of their usage. So, potentially
> > > > in the future, at the moment when .suspend() is called it might be disabled
> > > > (for example, .enable/disable() callbacks can be added and, if ARM Global timer
> > > > will not be registered as sched_clock, it will be possible to keep it disabled
> > > > if not used now).
> > > >
> > > > But It's not essentially now - I can update it and drop save restore.
> > > > Pls, confirm.
> > >
> > > I think it's best to skip suspend completely. You're not restoring
> > > anything you saved during suspend, unless you meant | where you used &.
> >
> > I didn't get it - I'm restoring one bit(0) only.
>
> that's the point, if you know you're restoring only that bit. Why save
> anything at all ?

i think there are difference between "restoring" and "re-enabling".
"restoring" - assume saving smth.. then restore saving value.
I'm saving & restoring one bit here.

But I can do just "re-enabling" -
  writel(GT_CONTROL_TIMER_ENABLE, gt_base + GT_CONTROL);
and then I don't need to save anything. It will work with current
code.

--
regards,
-grygorii
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