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

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Date:	Fri, 13 Nov 2015 11:40:47 -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>, 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:
> On 11/13/2015 06:43 PM, Felipe Balbi wrote:
>> 
>> 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 ?
>
> 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 &.

-- 
balbi

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