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

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Message-ID: <87si49ojed.fsf@saruman.tx.rr.com>
Date:	Fri, 13 Nov 2015 12:15:38 -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 07:40 PM, Felipe Balbi wrote:
>>
>> 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 &.
>>
>
> 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 ?

-- 
balbi

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