linux-kernel - Re: [PATCH] clocksource: arm_global

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Date:	Fri, 13 Nov 2015 10:43:39 -0600
From:	Felipe Balbi <balbi@...com>
To:	Grygorii Strashko <grygorii.strashko@...com>,
	<linux@....linux.org.uk>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Srinivas Kandagatla <srinivas.kandagatla@...il.com>,
	Maxime Coquelin <maxime.coquelin@...com>
CC:	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <kernel@...inux.com>,
	<linux-omap@...r.kernel.org>,
	Grygorii Strashko <grygorii.strashko@...com>,
	Arnd Bergmann <arnd@...db.de>,
	John Stultz <john.stultz@...aro.org>,
	Tony Lindgren <tony@...mide.com>
Subject: Re: [PATCH] clocksource: arm_global_timer: fix suspend resume


Hi,

Grygorii Strashko <grygorii.strashko@...com> 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@...db.de>
> Cc: John Stultz <john.stultz@...aro.org>
> Cc: Felipe Balbi <balbi@...com>
> Cc: Tony Lindgren <tony@...mide.com>
> Signed-off-by: Grygorii Strashko <grygorii.strashko@...com>
> ---
>  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 ?

-- 
balbi

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