linux-kernel - Re: [PATCH v2 4/6] msm: timer: SMP timer support for msm

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Message-ID: <20101208163956.GO9777@n2100.arm.linux.org.uk>
Date:	Wed, 8 Dec 2010 16:39:56 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Jeff Ohlstein <johlstei@...eaurora.org>
Cc:	Daniel Walker <dwalker@...eaurora.org>,
	linux-arm-msm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Brian Swetland <swetland@...gle.com>,
	Dima Zavin <dima@...roid.com>,
	Arve Hj�nnev�g <arve@...roid.com>,
	David Brown <davidb@...eaurora.org>,
	Bryan Huntsman <bryanh@...eaurora.org>,
	Stepan Moskovchenko <stepanm@...eaurora.org>,
	Gregory Bean <gbean@...eaurora.org>,
	Steve Muckle <smuckle@...eaurora.org>
Subject: Re: [PATCH v2 4/6] msm: timer: SMP timer support for msm

On Tue, Dec 07, 2010 at 08:28:19PM -0800, Jeff Ohlstein wrote:
> Signed-off-by: Jeff Ohlstein <johlstei@...eaurora.org>

I think Thomas' comments still apply to this patch.  In addition:

> @@ -65,49 +78,67 @@ struct msm_clock {
>  	void __iomem                *regbase;
>  	uint32_t                    freq;
>  	uint32_t                    shift;
> +	void                        *global_counter;
> +	void                        *local_counter;

These seem to be mmio addresses, so they should be 'void __iomem *' not
just 'void *'.

>  };
>  
> +enum {
> +	MSM_CLOCK_GPT,
> +	MSM_CLOCK_DGT,
> +	NR_TIMERS,
> +};

If these are supposed to be indexes to msm_clocks[], then please use
them as explicit array initializers in there - it adds useful
documentation so its not necessary to search around to find out
what's going on.

> -static cycle_t msm_gpt_read(struct clocksource *cs)
> +static cycle_t msm_read_timer_count(struct clocksource *cs)
>  {
> -	return readl(MSM_GPT_BASE + TIMER_COUNT_VAL);
> +	struct msm_clock *clk = container_of(cs, struct msm_clock, clocksource);
> +
> +	return readl(clk->global_counter) >> clk->shift;
>  }

Err.  This is what the core clocksource code does:

        cycle_now = tc->cc->read(tc->cc);

        /* calculate the delta since the last timecounter_read_delta(): */
        cycle_delta = (cycle_now - tc->cycle_last) & tc->cc->mask;

        /* convert to nanoseconds: */
        ns_offset = cyclecounter_cyc2ns(tc->cc, cycle_delta);

static inline u64 cyclecounter_cyc2ns(const struct cyclecounter *cc,
                                      cycle_t cycles)
{
        u64 ret = (u64)cycles;
        ret = (ret * cc->mult) >> cc->shift;
        return ret;

So doesn't this result in shifting left twice?

> +#ifdef CONFIG_SMP
> +void local_timer_setup(struct clock_event_device *evt)
> +{
> +	unsigned long flags;
> +	struct msm_clock *clock = &msm_clocks[MSM_GLOBAL_TIMER];
> +
> +	writel(DGT_CLK_CTL_DIV_4, MSM_TMR_BASE + DGT_CLK_CTL);
> +
> +	if (!local_clock_event) {
> +		writel(0, clock->regbase  + TIMER_ENABLE);
> +		writel(0, clock->regbase + TIMER_CLEAR);
> +		writel(~0, clock->regbase + TIMER_MATCH_VAL);
> +	}
> +	evt->irq = clock->irq.irq;
> +	evt->name = "local_timer";
> +	evt->features = CLOCK_EVT_FEAT_ONESHOT;
> +	evt->rating = clock->clockevent.rating;
> +	evt->set_mode = msm_timer_set_mode;
> +	evt->set_next_event = msm_timer_set_next_event;
> +	evt->shift = clock->clockevent.shift;
> +	evt->mult = div_sc(clock->freq, NSEC_PER_SEC, evt->shift);
> +	evt->max_delta_ns =
> +		clockevent_delta2ns(0xf0000000 >> clock->shift, evt);
> +	evt->min_delta_ns = clockevent_delta2ns(4, evt);
> +	evt->cpumask = cpumask_of(smp_processor_id());
> +
> +	local_clock_event = evt;
> +
> +	local_irq_save(flags);
> +	get_irq_chip(clock->irq.irq)->unmask(clock->irq.irq);
> +	local_irq_restore(flags);

I can't make out what the situation is here.  Are you using what is a
local timer on CPU0 as a global timer?
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