[PATCH 1/2] clocksource/drivers/lpc32xx: Support periodic mode

[Joachim Eastwood]

On 1 February 2016 at 16:09, Ezequiel Garcia
<ezequiel at vanguardiasur.com.ar> wrote:
> On 31 January 2016 at 17:07, Ezequiel Garcia
> <ezequiel at vanguardiasur.com.ar> wrote:
>> On 30 January 2016 at 16:39, Joachim  Eastwood <manabian at gmail.com> wrote:
>>> Hi Ezequiel,
>>>
>>> On 30 January 2016 at 07:46, Ezequiel Garcia
>>> <ezequiel at vanguardiasur.com.ar> wrote:
>>>> This commit adds the support for periodic mode. This is done by not
>>>> setting the MR0S (Stop on TnMR0) bit on MCR, thus allowing
>>>> interrupts to be periodically generated on MR0 matches.
>>>>
>>>> In order to do this, move the initial configuration that is specific to
>>>> the one shot mode to clock_event_device.set_state_oneshot.
>>>>
> [...]
>>
>>>
>>> I will look more closely at the new timer setup later.
>>>
>>> btw, didn't I look through a version of this you sent me privately
>>> quite some time ago?
>>> I think I had a comment about using TIMER_PR instead of TIMER_MR0
>>> then. Unsure if that is still valid, though.
>>>
>>
>> Ah, right. It was ages ago, and forgot your previous review. Sorry about that.
>> Using TIMER_PR looks less invasive so I'll send a v2 using it instead.
>
> Actually, using the prescale counter and MR0 = 1 resulted in exactly
> half the number of interrupts that I expected (HZ / 2). Using this
> patch, with PR=0 and MR0=ticks_per_jiggies, I can see HZ no. of
> interrupts per sec.
>
> Why did you choose to use the prescale in your oneshot implementation?

The clockevent code was copied from arch/arm/mach-lpc32xx/timer.c so
it's really old code.
I think it is a strange way to use the timer, but the logic still
seems good to me.

> Did you test or measure the timer expire using the PR and MR0 = 1?

I really can't remember. I do remember going through the timer setup
and it seemed like a valid, albeit slightly strange, way to use the
timer.

> To be honest, I'm still trying to make some sense out of my results.

I'll see if can find the time to do some more testing over here as well.


regards,
Joachim Eastwood