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?
Regards,
Jean
>
> Reported-by: Jon Hunter <jon-hunter@xxxxxx>
> Signed-off-by: Kevin Hilman <khilman@xxxxxxxxxxxxxxxxxxx>
> ---
> 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
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