On 07.07.2016 13:53, Peter Maydell wrote:
> On 4 July 2016 at 10:55, Peter Maydell <peter.mayd...@linaro.org> wrote:
>> On 1 July 2016 at 18:49, Dmitry Osipenko <dig...@gmail.com> wrote:
>>> On 01.07.2016 19:36, Peter Maydell wrote:
>>>> On 30 June 2016 at 20:01, Dmitry Osipenko <dig...@gmail.com> wrote:
>>>>> On 30.06.2016 18:02, Peter Maydell wrote:
>>>>>> What I meant was: ptimer_get_count() is typically called to generate
>>>>>> a value to return from a register. That's a separate thing, conceptually,
>>>>>> from whether the device happens to also trigger an interrupt on timer
>>>>>> expiry by passing a bh to ptimer_init(). So it's very odd for a detail
>>>>>> of interrupt-on-timer-expiry (that there is a bottom half) to affect
>>>>>> the value returned when you read the timer count register.
>>>>
>>>>> In order to handle wraparound correctly, software needs to track the
>>>>> moment of
>>>>> the wraparound - the interrupt. If software reads wrapped around counter
>>>>> value
>>>>> before IRQ triggered (ptimer expired), then it would assume that no
>>>>> wraparound
>>>>> happened and won't perform counter value correction, resulting in periodic
>>>>> counter "jumping" backwards.
>>>>
>>>> That just says you need particular behaviour between counter reads
>>>> and IRQ triggers; it doesn't say that you need the behaviour to be
>>>> different if the ptimer code doesn't know about the IRQ trigger.
>>>>
>>>
>>> Okay, I already explained the reason for having two different behaviours -
>>> to
>>> make polled counter value more distributed when possible. If I understand
>>> you
>>> correctly, you don't like it because it is "odd" and I agree that it's a
>>> bit clumsy.
>>
>>> So, what we are going to do now? Would you just revert the offending commit
>>> or
>>> you have some other suggestions?
>>
>> Well, we need to fix the regression, but basically I'm kind of
>> confused at the moment. I haven't invested a lot of time in
>> trying to understand the timer code, so all I can really do
>> is say "this does not look like the right thing" and ask you
>> to come up with a different fix for it.
>
I'm currently leaning to the revert solution. Unfortunately, I haven't had a
chance to look at it yet, will do it today and send patch after.
> My current best guess is that this condition should simply be
> "if (expired) {".
>
Since you are insisted that wraparound isn't a needed feature - yes, that's
nearly the same what the original code did :)
--
Dmitry
