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    SubjectRe: [PATCH v2 22/44] metag: Time keeping
    On 04/01/13 10:05, Vineet Gupta wrote:
    > Hi James,
    >
    > On Wednesday 05 December 2012 09:38 PM, James Hogan wrote:
    >
    >> +static unsigned int hwtimer_freq = HARDWARE_FREQ;
    >> +static DEFINE_PER_CPU(struct clock_event_device, local_clockevent);
    >> +static DEFINE_PER_CPU(char [11], local_clockevent_name);
    >
    >> +void __cpuinit local_timer_setup(unsigned int cpu)
    >> +{
    >> + unsigned int txdivtime;
    >> + struct clock_event_device *clk = &per_cpu(local_clockevent, cpu);
    >> + char *name = per_cpu(local_clockevent_name, cpu);
    >> +
    >> + txdivtime = TBI_GETREG(TXDIVTIME);
    >> +
    >> + txdivtime &= ~TXDIVTIME_DIV_BITS;
    >> + txdivtime |= (HARDWARE_DIV & TXDIVTIME_DIV_BITS);
    >> +
    >> + TBI_SETREG(TXDIVTIME, txdivtime);
    >> +
    >> + sprintf(name, "META %d", cpu);
    >> + clk->name = name;
    >> + clk->features = CLOCK_EVT_FEAT_ONESHOT,
    >> +
    >> + clk->rating = 200,
    >> + clk->shift = 12,
    >> + clk->irq = TBID_SIGNUM_TRT,
    >> + clk->set_mode = metag_timer_set_mode,
    >> + clk->set_next_event = metag_timer_set_next_event,
    >> +
    >> + clk->mult = div_sc(hwtimer_freq, NSEC_PER_SEC, clk->shift);
    >> + clk->max_delta_ns = clockevent_delta2ns(0x7fffffff, clk);
    >> + clk->min_delta_ns = clockevent_delta2ns(0xf, clk);
    >> + clk->cpumask = cpumask_of(cpu);
    >> +
    >> + clockevents_register_device(clk);
    >> +
    >> + /*
    >> + * For all non-boot CPUs we need to synchronize our free
    >> + * running clock (TXTIMER) with the boot CPU's clock.
    >> + *
    >> + * While this won't be accurate, it should be close enough.
    >> + */
    >> + if (cpu) {
    >> + unsigned int thread0 = cpu_2_hwthread_id[0];
    >> + unsigned long val;
    >> +
    >> + val = core_reg_read(TXUCT_ID, TXTIMER_REGNUM, thread0);
    >> +
    >> + asm volatile("MOV TXTIMER, %0\n" : : "r" (val));
    >> + }
    >> +}
    >> +
    >> +void __init time_init(void)
    >> +{
    >> + /*
    >> + * On Meta 2 SoCs, the actual frequency of the timer is based on the
    >> + * Meta core clock speed divided by an integer, so it is only
    >> + * approximately 1MHz. Calculating the real frequency here drastically
    >> + * reduces clock skew on these SoCs.
    >> + */
    >> +#ifdef CONFIG_METAG_META21
    >> + hwtimer_freq = get_coreclock() / (metag_in32(EXPAND_TIMER_DIV) + 1);
    >> +#endif
    >> + clocksource_register_hz(&clocksource_metag, hwtimer_freq);
    >> +
    >> + setup_irq(TBID_SIGNUM_TRT, &metag_timer_irq);
    >> +
    >> + local_timer_setup(smp_processor_id());
    >> +}
    >
    > I have a kludge in ARC port in this subsystem - which I hope you could help clear.
    >
    > ARC also has a local timer device used for clockevent on each CPU. A one-time
    > setup_irq() with IRQF_PERCPU - would indeed setup the generic IRQ subsystem - for
    > making registration effective for all CPUs. However don't you need some per-cpu
    > magic - say enabling the IRQ at cpu or embedded interrupt controller level -
    > assuming you starts off with all IRQs disabled (which ARC Linux does).

    Hi Vineet,

    For Meta this is done in secondary_start_kernel in
    arch/metag/kernel/smp.c (see
    https://github.com/jahogan/metag-linux/blob/metag-core/arch/metag/kernel/smp.c#L276).
    It uses tbi_startup_interrupt which is also called by the irq_startup
    callback for the root irq_chip.

    > So we end up using different APIs - request_percpu_irq() as equivalent of
    > setup_irq() on boot-cpu only and then each CPU calling enable_percpu_irq() to do
    > the local magic. request_percpu_irq() in turn requires an apriori call to
    > irq_set_percpu_devid().

    For Meta we could probably do something similar if we moved it's root
    irq_startup irq_chip callback code into irq_enable or irq_unmask.

    Cheers
    James

    >
    > https://lkml.org/lkml/2012/11/7/128
    >
    > Do don't seem to be requiring all of this hence I'm wondering how it works for you!
    >
    > -Vineet
    >



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