Re: [PATCH] clocksource: arm_global_timer: fix suspend resume

[Grygorii Strashko]

Hi Felipe,
On 11/13/2015 08:59 PM, Grygorii Strashko wrote:
> On 11/13/2015 08:32 PM, Felipe Balbi wrote:
>> Grygorii Strashko <grygorii.strashko@xxxxxx> writes:
>>> On 11/13/2015 08:15 PM, Felipe Balbi wrote:
>>>> Grygorii Strashko <grygorii.strashko@xxxxxx> writes:
>>>>> On 11/13/2015 07:40 PM, Felipe Balbi wrote:
>>>>>> Grygorii Strashko <grygorii.strashko@xxxxxx> writes:
>>>>>>> On 11/13/2015 06:43 PM, Felipe Balbi wrote:
>>>>>>>> GrygoCONFIG_CLKSRC_ARM_GLOBAL_TIMER_SCHED_CLOCKrii Strashko <grygorii.strashko@xxxxxx> 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@xxxxxxxx>
>>>>>>>>> Cc: John Stultz <john.stultz@xxxxxxxxxx>
>>>>>>>>> Cc: Felipe Balbi <balbi@xxxxxx>
>>>>>>>>> Cc: Tony Lindgren <tony@xxxxxxxxxxx>
>>>>>>>>> Signed-off-by: Grygorii Strashko <grygorii.strashko@xxxxxx>
>>>>>>>>> ---
>>>>>>>>>       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.
>>
> 
> I'm writing:
> gt_control & GT_CONTROL_TIMER_ENABLE, where gt_control is old value of GT_CONTROL
> before entering suspend, so on resume:
>   - if gt_control == 0x0000 0001 ==> gt_control & GT_CONTROL_TIMER_ENABLE(0x1) == 0x1
>   - if gt_control == 0x0000 0000 ==> gt_control & GT_CONTROL_TIMER_ENABLE(0x1) == 0x0
> 
> What am I missed?
> 

Any way, I'll wait for other comments a bit, replace save/restore with
just pure re-enabling and re-send.

Thanks.

-- 
regards,
-grygorii
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