[RFC PATCHv2] picoxcell: add support for the system timers

[Russell King - ARM Linux]

On Fri, Nov 26, 2010 at 11:11:16AM +0000, Jamie Iles wrote:
> +static irqreturn_t timer_interrupt(int irq, void *dev_id)
> +{
> +	struct timer_instance *timer = &timers[TIMER_ID_CLOCKEVENT];
> +
> +	/* If we are in oneshot mode, we need to stop receiving interrupts. */
> +	if (CLOCK_EVT_MODE_ONESHOT == clockevent_picoxcell.mode) {
> +		unsigned long val = readl(timer->base +
> +					  TIMER_CONTROL_REG_OFFSET);
> +		val |= TIMER_INTERRUPT_MASK;
> +		writel(val, timer->base + TIMER_CONTROL_REG_OFFSET);
> +	}

It's normal not to emulate behaviours here which the hardware doesn't
support - that's the point of the generic clockevents/clocksource
layers.  They're there to handle whatever the hardware can support and
turn it into something the kernel wants.

> +/*
> + * Overwrite weak default sched_clock with something more precise.
> + *
> + * On picoXcell we have a RTC that clocks at 200MHz so a multiply by 5 gives
> + * us a nanosecond count.
> + */
> +unsigned long long notrace sched_clock(void)
> +{
> +#define CYCLES_TO_NSEC_MULT	(NSEC_PER_SEC / CLOCK_TICK_RATE)
> +	return cnt32_to_63(readl(IO_ADDRESS(PICOXCELL_RTCLK_BASE) +
> +				 RTCLK_CCV_REG_OFFSET)) * CYCLES_TO_NSEC_MULT;

Have you read the comments in include/linux/cnt32_to_63.h, or thought
about the '63' part of the name ?