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

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Date:	Fri, 13 Nov 2015 20:09:06 +0200
From:	Grygorii Strashko <grygorii.strashko@...com>
To:	Felipe Balbi <balbi@...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

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.

-- 
regards,
-grygorii
--
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