linux-kernel - Re: [PATCH v5 5/5] drivers: clocksource: add CPU PM notifier for ARM architected timer

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Date:	Thu, 19 Feb 2015 13:03:57 +0000 (UTC)
From:	Venkappa Mala <venkappa.m@...sung.com>
To:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 5/5] drivers: clocksource: add CPU PM notifier for ARM architected timer

Sudeep KarkadaNagesha <Sudeep.KarkadaNagesha <at> arm.com> writes:

> 
> On 28/08/13 11:44, Sudeep KarkadaNagesha wrote:
> > From: Sudeep KarkadaNagesha <sudeep.karkadanagesha <at> arm.com>
> > 
> > Few control settings done in architected timer as part of 
initialisation
> > can be lost when CPU enters deeper power states. They need to be
> > re-initialised when the CPU is (warm)reset again.
> > 
> > This patch adds CPU PM notifiers to do the timer initialisation on 
warm
> > resets. It also save the event stream divider value calculated 
during
> > cold reset and uses the same in warm reset path.
> > 
> Ah, forgot to update the commit log. It's now updated:
> 
> Few control settings done in architected timer as part of 
initialisation
> can be lost when CPU enters deeper power states. They need to be
> restored when the CPU is (warm)reset again.
> 
> This patch adds CPU PM notifiers to save the counter control register
> when entering low power modes and restore it when CPU exits low power.
> 
> > Cc: Catalin Marinas <catalin.marinas <at> arm.com>
> > Reviewed-by: Lorenzo Pieralisi <lorenzo.pieralisi <at> arm.com>
> > Reviewed-by: Will Deacon <will.deacon <at> arm.com>
> > Signed-off-by: Sudeep KarkadaNagesha <sudeep.karkadanagesha <at> 
arm.com>
> > ---
> >  drivers/clocksource/arm_arch_timer.c | 34 
++++++++++++++++++++++++++++++++++
> >  1 file changed, 34 insertions(+)
> > 
> > diff --git a/drivers/clocksource/arm_arch_timer.c 
b/drivers/clocksource/arm_arch_timer.c
> > index f42bef4..ffb0bfb 100644
> > --- a/drivers/clocksource/arm_arch_timer.c
> > +++ b/drivers/clocksource/arm_arch_timer.c
> >  <at>  <at>  -13,6 +13,7  <at>  <at> 
> >  #include <linux/device.h>
> >  #include <linux/smp.h>
> >  #include <linux/cpu.h>
> > +#include <linux/cpu_pm.h>
> >  #include <linux/clockchips.h>
> >  #include <linux/interrupt.h>
> >  #include <linux/of_irq.h>
> >  <at>  <at>  -281,6 +282,33  <at>  <at>  static struct 
notifier_block arch_timer_cpu_nb = {
> >  	.notifier_call = arch_timer_cpu_notify,
> >  };
> >  
> > +#ifdef CONFIG_CPU_PM
> > +static unsigned int saved_cntkctl;
> > +static int arch_timer_cpu_pm_notify(struct notifier_block *self,
> > +				    unsigned long action, void *hcpu)
> > +{
> > +	if (action == CPU_PM_ENTER)
> > +		saved_cntkctl = arch_timer_get_cntkctl();
> > +	else if (action == CPU_PM_ENTER_FAILED || action == CPU_PM_EXIT)
> > +		arch_timer_set_cntkctl(saved_cntkctl);
> > +	return NOTIFY_OK;
> > +}
> > +
> > +static struct notifier_block arch_timer_cpu_pm_notifier = {
> > +	.notifier_call = arch_timer_cpu_pm_notify,
> > +};
> > +
> > +static int __init arch_timer_cpu_pm_init(void)
> > +{
> > +	return cpu_pm_register_notifier(&arch_timer_cpu_pm_notifier);
> > +}
> > +#else
> > +static int __init arch_timer_cpu_pm_init(void)
> > +{
> > +	return 0;
> > +}
> > +#endif
> > +
> >  static int __init arch_timer_register(void)
> >  {
> >  	int err;
> >  <at>  <at>  -330,11 +358,17  <at>  <at>  static int __init 
arch_timer_register(void)
> >  	if (err)
> >  		goto out_free_irq;
> >  
> > +	err = arch_timer_cpu_pm_init();
> > +	if (err)
> > +		goto out_unreg_notify;
> > +
> >  	/* Immediately configure the timer on the boot CPU */
> >  	arch_timer_setup(this_cpu_ptr(arch_timer_evt));
> >  
> >  	return 0;
> >  
> > +out_unreg_notify:
> > +	unregister_cpu_notifier(&arch_timer_cpu_nb);
> >  out_free_irq:
> >  	if (arch_timer_use_virtual)
> >  		free_percpu_irq(arch_timer_ppi[VIRT_PPI], 
arch_timer_evt);
> > 
> 
> 

Hello Catalin,

I have noticed this patch merge in 
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git 
at >= linux-3.13.y branches.

As part of ARMv7/ARMv8 vDSO experiments, i have tried to enable arch 
timer in 3.10 branch but it is failed to boot like 
"[1246696886.455361]      swapper/0:    0] [c0] [c0] Calibrating delay 
loop (skipped), value calculated using timer frequency.. 52.00 BogoMIPS 
(lpj=260000)" 
due to cntkctl context lost on both armv7/armv8 cases.However, it works 
fine when I have pulled the patch to 3.10 branch.

Perhaps, it will be good to have this patch in 3.10.y (LTS kernel) 
branch as well.
is there any potential issue if we merge this patch or is it 
intentional?

BR,
Venkappa



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