linux-kernel - Re: [PATCH 4/4] drivers: clocksource: add CPU PM notifier for ARM architected timer

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Date:	Tue, 02 Jul 2013 17:09:41 +0100
From:	"Jon Medhurst (Tixy)" <tixy@...aro.org>
To:	Sudeep KarkadaNagesha <Sudeep.KarkadaNagesha@....com>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	mark.rutland@....com, linux@....linux.org.uk,
	catalin.marinas@....com, will.deacon@....com, marc.zyngier@....com,
	tglx@...utronix.de
Subject: Re: [PATCH 4/4] drivers: clocksource: add CPU PM notifier for ARM
 architected timer

On Tue, 2013-06-18 at 18:07 +0100, Sudeep KarkadaNagesha wrote:
> From: Sudeep KarkadaNagesha <sudeep.karkadanagesha@....com>
> 
> Few control settings done in architected timer as part of initialisation
> are lost when CPU enters deeper power states. They need to be re-initialised
> when the CPU is (warm)reset again.
> 
> This patch moves all such initialisation into separate function that can
> be used both in cold and warm CPU reset paths. It also adds CPU PM
> notifiers to do the timer initialisation on warm resets.
> 
> Signed-off-by: Sudeep KarkadaNagesha <sudeep.karkadanagesha@....com>
> Reviewed-by: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
> Reviewed-by: Will Deacon <will.deacon@....com>
> ---
>  drivers/clocksource/arm_arch_timer.c | 51 +++++++++++++++++++++++++++++++-----
>  1 file changed, 44 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index 11aaf06..1c691b1 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -13,6 +13,7 @@
>  #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>
> @@ -123,10 +124,20 @@ static int arch_timer_set_next_event_phys(unsigned long evt,
>  	return 0;
>  }
>  
> -static int __cpuinit arch_timer_setup(struct clock_event_device *clk)
> +static void arch_timer_initialise(void)
>  {
>  	int evt_stream_div, pos;
>  
> +	/* Find the closest power of two to the divisor */
> +	evt_stream_div = arch_timer_rate / ARCH_TIMER_EVT_STREAM_FREQ;
> +	pos = fls(evt_stream_div);
> +	if (pos > 1 && !(evt_stream_div & (1 << (pos - 2))))
> +		pos--;
> +	arch_counter_set_user_access(min(pos, 15));

Would it not be good to calculate the value once in arch_timer_setup
rather than repeatedly in this function? The calculations aren't that
expensive, but when I gave these patches a spin on TC2 I noticed that
this function gets called >500 times a second, so it seems a bit
wasteful.

> +}
> +
> +static int __cpuinit arch_timer_setup(struct clock_event_device *clk)
> +{
>  	clk->features = CLOCK_EVT_FEAT_ONESHOT | CLOCK_EVT_FEAT_C3STOP;
>  	clk->name = "arch_sys_timer";
>  	clk->rating = 450;
> @@ -155,12 +166,7 @@ static int __cpuinit arch_timer_setup(struct clock_event_device *clk)
>  			enable_percpu_irq(arch_timer_ppi[PHYS_NONSECURE_PPI], 0);
>  	}
>  
> -	/* Find the closest power of two to the divisor */
> -	evt_stream_div = arch_timer_rate / ARCH_TIMER_EVT_STREAM_FREQ;
> -	pos = fls(evt_stream_div);
> -	if (pos > 1 && !(evt_stream_div & (1 << (pos - 2))))
> -		pos--;
> -	arch_counter_set_user_access(min(pos, 15));
> +	arch_timer_initialise();
>  
>  	return 0;
>  }
> @@ -267,6 +273,31 @@ static struct notifier_block arch_timer_cpu_nb __cpuinitdata = {
>  	.notifier_call = arch_timer_cpu_notify,
>  };
>  
> +#ifdef CONFIG_CPU_PM
> +static int arch_timer_cpu_pm_notify(struct notifier_block *self,
> +				    unsigned long action, void *hcpu)
> +{
> +	if (action == CPU_PM_EXIT)
> +		arch_timer_initialise();
> +
> +	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;
> @@ -316,11 +347,17 @@ 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);

-- 
Tixy

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