[PATCH 1/3] ARM: S5P: Add s5p_timer support for HRT

[Linus Walleij]

2011/2/26 Sangbeom Kim <sbkim73 at samsung.com>:
> (...)
> +static void s5p_clockevent_init(void)
> +{
> +       unsigned long pclk;
> +       unsigned long clock_rate;
> +       unsigned int irq_number;
> +       struct clk *tscaler;
> +
> +       pclk = clk_get_rate(timerclk);
> +
> +       tscaler = clk_get_parent(tdiv_event);
> +
> +       clk_set_rate(tscaler, pclk / 2);
> +       clk_set_rate(tdiv_event, pclk / 2);
> +       clk_set_parent(tin_event, tdiv_event);
> +
> +       clock_rate = clk_get_rate(tin_event);
> +       clock_count_per_tick = clock_rate / HZ;
> +
> +       time_event_device.mult =
> +               div_sc(clock_rate, NSEC_PER_SEC, time_event_device.shift);
> +       time_event_device.max_delta_ns =
> +               clockevent_delta2ns(-1, &time_event_device);
> +       time_event_device.min_delta_ns =
> +               clockevent_delta2ns(1, &time_event_device);

This is a very complicated and inprecise way of doing this nowadays.
Skip hardcoding the shift value and calculating mult like that and use

/* Be able to sleep for atleast 4 seconds (usually more) */
#define EVT_MIN_RANGE 4

clockevents_calc_mult_shift(&time_event_device,
                                    clock_rate, EVT_MIN_RANGE);

> (...)
> +static void s5p_clocksource_init(void)
> +{
> +       unsigned long pclk;
> +       unsigned long clock_rate;
> +
> +       pclk = clk_get_rate(timerclk);
> +
> +       clk_set_rate(tdiv_source, pclk / 2);
> +       clk_set_parent(tin_source, tdiv_source);
> +
> +       clock_rate = clk_get_rate(tin_source);
> +
> +       s5p_time_setup(timer_source.source_id, TCNT_MAX);
> +       s5p_time_start(timer_source.source_id, PERIODIC);
> +
> +       if (clocksource_register_hz(&time_clocksource, clock_rate))
> +               panic("%s: can't register clocksource\n", time_clocksource.name);
> +}

This is more like it :-)

But you probably also want to add a sched_clock hook for this
platform too, so you get some nice scheduling resolution.

I suggest you look at the simple straight-forward driver
for U300 in arch/arm/mach-u300/timer.c for inspiration.
It's using the same timer that is used for clocksource for
sched_clock().


Yours,
Linus Walleij