[PATCH 05/10] [ARM] tegra: Add timer support

[Colin Cross]

On Mon, Jun 7, 2010 at 4:43 PM, Linus Walleij
<linus.ml.walleij at gmail.com> wrote:
> 2010/6/4 Olof Johansson <olof at lixom.net>:
>
>> (....)
>> +static struct clock_event_device tegra_clockevent = {
>> +       .name           = "timer0",
>> +       .rating         = 300,
>> +       .features       = CLOCK_EVT_FEAT_ONESHOT | CLOCK_EVT_FEAT_PERIODIC,
>> +       .mult           = 16777,
>> +       .shift          = 24,
>> +       .set_next_event = tegra_timer_set_next_event,
>> +       .set_mode       = tegra_timer_set_mode,
>> +};
>> +
>> +static struct clocksource tegra_clocksource = {
>> +       .name   = "timer_us",
>> +       .rating = 300,
>> +       .read   = tegra_clocksource_read,
>> +       .mask   = 0xFFFFFFFFUL,
>> +       .mult   = 1000,
>> +       .shift  = 0,
>> +       .flags  = CLOCK_SOURCE_IS_CONTINUOUS,
>> +};
>
> How did you calculate the magic mult/shift numbers 16777/24 and
> 1000/0 above? Especially the latter intuitively seem very inappropriate,
> and I guess there will be revisions of this platform with new frequencies
> for the timer as well, making these hard-coded values a bug source.

Thanks, fixed.  The numbers are correct, as Tegra timers all run at
1MHz regardless of input clock frequency, but removing the magic
numbers is clearer.

For the clocksource, I replaced it with clocksource_register_hz, which
hides the minsec number as well. Clockevents I replaced iwth
clockevents_calc_mult_shift.

> I would consider using the
> clocksource_calc_mult_shift() and
> clockevents_calc_mult_shift()
> functions based on the frequency of the timer counter and a minimum wakeup
> range if you don't know exactly why you want these mult+shifts.
>
> I posted some patches to encourage the use of these recently.
>
> Yours,
> Linus Walleij
>