Re: [PATCH v2] OMAP: timekeeping: time should not stop during suspend

[Kevin Hilman <khilman@deeprootsystems.com>]

Tony Lindgren <tony@atomide.com> writes:

> * Kevin Hilman <khilman@deeprootsystems.com> [091117 15:41]:
>> During suspend, the kernel timekeeping subsystem is shut down.  Before
>> suspend and upon resume, it uses a weak function
>> read_persistent_clock() to determine the amount of time that elapsed
>> during suspend.
>> 
>> This function was not implemented on OMAP, so from the timekeeping
>> subsystem perspective (and thus userspace as well) it appeared that no
>> time elapsed during suspend.
>> 
>> This patch uses the 32k sync timer as a the persistent clock the 32k
>> sync timer value converted to seconds.
>> 
>> NOTE: This does *NOT* handle wrapping of the 32k sync timer, so
>>       wrapping of the 32k sync timer during suspend may cause
>>       problems.  Also, there are not interrupts when the 32k sync
>>       timer wraps, so something else has to be done.
>
> Kevin, are you planning to queue this in your PM series for the next
> merge window? In that case Acked-by: Tony Lindgren <tony@atomide.com>
>
> If you want me to queue this as a fix for the -rc series, let me know.

I'll queue it for next merge window, thanks.

Kevin

>  
>> Reported-by: Jon Hunter <jon-hunter@ti.com>
>> Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>
>> ---
>> Since v1 of this patch, the signature of this function changed.
>> 
>> Also note that forthcoming omap_device patches will depend on this
>> function instead of getnstimeofday() since the timekeeping subsystem
>> is suspended when we want to do omap_device timing measurements.
>> 
>>  arch/arm/plat-omap/common.c |   19 +++++++++++++++++++
>>  1 files changed, 19 insertions(+), 0 deletions(-)
>> 
>> diff --git a/arch/arm/plat-omap/common.c b/arch/arm/plat-omap/common.c
>> index cc050b3..8057966 100644
>> --- a/arch/arm/plat-omap/common.c
>> +++ b/arch/arm/plat-omap/common.c
>> @@ -172,6 +172,25 @@ unsigned long long sched_clock(void)
>>  				  clocksource_32k.mult, clocksource_32k.shift);
>>  }
>>  
>> +/**
>> + * read_persistent_clock -  Return time from the persistent clock.
>> + *
>> + * Reads the time from a source which isn't disabled during PM: 32k sync
>> + * Returns a timespec with tv_sec=0 and tv_nsec=0 if unsupported.
>> + *
>> + */
>> +void read_persistent_clock(struct timespec *ts)
>> +{
>> +	unsigned long long nsecs;
>> +	cycle_t cycles;
>> +
>> +	ts->tv_sec = ts->tv_nsec = 0;
>> +	cycles = clocksource_32k.read(&clocksource_32k);
>> +	nsecs = clocksource_cyc2ns(cycles,
>> +				   clocksource_32k.mult, clocksource_32k.shift);
>> +	timespec_add_ns(ts, nsecs);
>> +}
>> +
>>  static int __init omap_init_clocksource_32k(void)
>>  {
>>  	static char err[] __initdata = KERN_ERR
>> -- 
>> 1.6.5.1
>> 
>> --
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