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    SubjectRe: [PATCH v2 22/44] metag: Time keeping
    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).

    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().

    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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