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

[Tony Lindgren <tony@atomide.com>]

* 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.

Regards,

Tony
 
> 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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