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

[Kevin Hilman <khilman@deeprootsystems.com>]

Jean Pihet <jpihet@mvista.com> writes:

> Kevin,
>
> On Friday 25 September 2009 01:35:48 Kevin Hilman wrote:
>> 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.
> I think we should read the 32k timer value before entering the sleep and 
> reading it again at resume time. Doing so up to one overflow could be 
> handled, which means a maximum sleep period of 36.4 hours.
>
> Now the time wrap problem imposes the system to wake-up before 36.4 hours. We 
> have a few options:
> 1) always use the wake-up timer with a wake-up time < 36.4 hours
> 2) rely on the user space to set the wake-up timer correctly, depending on the 
> applications needs.
>
> I am for option 1.
>
> Any thoughts?

I agree with option 1.

Kevin

>>
>> Reported-by: Jon Hunter <jon-hunter@ti.com>
>> Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>
>> ---
>> Tested on OMAP3 using PM branch.
>> If no issues, I will queue for 2.6.32-rc fixes
>>
>>  arch/arm/plat-omap/common.c |   15 +++++++++++++++
>>  1 files changed, 15 insertions(+), 0 deletions(-)
>>
>> diff --git a/arch/arm/plat-omap/common.c b/arch/arm/plat-omap/common.c
>> index b3f70e6..3e4325b 100644
>> --- a/arch/arm/plat-omap/common.c
>> +++ b/arch/arm/plat-omap/common.c
>> @@ -178,6 +178,21 @@ unsigned long long sched_clock(void)
>>  	return ret;
>>  }
>>
>> +/**
>> + * read_persistent_clock -  Return time in seconds from the persistent
>> clock. + */
>> +unsigned long read_persistent_clock(void)
>> +{
>> +	unsigned long long ret;
>> +	cycle_t cycles;
>> +
>> +	cycles = clocksource_32k.read(&clocksource_32k);
>> +	ret = (cycles * clocksource_32k.mult_orig) >> clocksource_32k.shift;
>> +	do_div(ret, NSEC_PER_SEC);
>> +
>> +	return (unsigned long)ret;
>> +}
>> +
>>  static int __init omap_init_clocksource_32k(void)
>>  {
>>  	static char err[] __initdata = KERN_ERR