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

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Message-ID: <87mvuhoimr.fsf@saruman.tx.rr.com>
Date:	Fri, 13 Nov 2015 12:32:12 -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 08:15 PM, Felipe Balbi wrote:
>>
>> 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 ?
>>
>
> i think there are difference between "restoring" and "re-enabling".
> "restoring" - assume saving smth.. then restore saving value.
> I'm saving & restoring one bit here.

with your current suspend/resume, they are the same thing. You save
GT_CONTROL contents, timer goes off and looses context, you set ENABLE
bit. No difference what so ever.

-- 
balbi

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