Messages in this thread | | | Date | Mon, 1 Aug 2011 10:42:35 +0200 | Subject | Re: [PATCH] Add sched_clock to AT91 TCB clocksource driver | From | Remy Bohmer <> |
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Hi Russell,
2011/7/31 Russell King - ARM Linux <linux@arm.linux.org.uk>: >> +++ b/arch/arm/Kconfig >> @@ -296,6 +296,7 @@ config ARCH_AT91 >> select HAVE_CLK >> select CLKDEV_LOOKUP >> select ARM_PATCH_PHYS_VIRT if MMU >> + select HAVE_SCHED_CLOCK if ATMEL_TCB_CLKSRC >> help >> This enables support for systems based on the Atmel AT91RM9200, >> AT91SAM9 and AT91CAP9 processors. >> diff --git a/arch/arm/kernel/sched_clock.c b/arch/arm/kernel/sched_clock.c >> index 9a46370..f9028e4 100644 >> --- a/arch/arm/kernel/sched_clock.c >> +++ b/arch/arm/kernel/sched_clock.c >> @@ -20,6 +20,13 @@ static void (*sched_clock_update_fn)(void); >> >> static void sched_clock_poll(unsigned long wrap_ticks) >> { >> + /* >> + * The sched_clock_update_fn may be initialised AFTER first call to >> + * time_init() >> + */ >> + if (unlikely(!sched_clock_update_fn)) >> + return; > > NAK. I've said this before - sched_clock _must_ be up and running by the > time this function is called - because shortly after this call is when > the scheduler initializes, and the scheduler wants sched_clock() working > at that point.
OK, I know that too, but the jiffies based fallback does it even worse, since it does not run at all... (It only updates in steps of a couple of 100msecs and stops after a while, and even does not display a real time...) This sched_clock implementation at least works before the drivers are being initialised...
Anyway, do you have a better suggestion how to fix this? The tcb clocksource is loaded during a arch_initcall(), perhaps we need something before that point. I do not see an easy way to integrate it in MACHINE_START(.timer). Would 'late_time_init' be a better solution?
Kind regards,
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