Re: [Qemu-arm] [PATCH v10 5/7] hw/ptimer: Legalize running with delta = load = 0

[Dmitry Osipenko <digetx@gmail.com>]

12.01.2016 21:12, Dmitry Osipenko пишет:
> 12.01.2016 06:58, Peter Crosthwaite пишет:
>> On Sat, Jan 09, 2016 at 08:39:53PM +0300, Dmitry Osipenko wrote:
>>> Currently ptimer would print error message and clear enable flag for an
>>> arming timer that has delta = load = 0. That actually could be a valid case
>>> for some hardware, like instant IRQ trigger for oneshot timer or continuous
>>> in periodic mode. Support those cases by printing error message only when
>>> period = 0.
>>>
>>
>> Isn't the continuous-periodic the same as period = 0, so if we were to really
>> support this, there should be no error message. This would simplify as we
>> can remove the conditionals of 0 period completely and rely only on the
>> too-fast clamps you add in previous patches.
>>
>
> I don't think that clamping is needed. Instead doing the ptimer_tick might be
> necessary, so ptimer user could handle that case on it own.
>
> BTW, that printf isn't quite reliable, hw_error or other way of execution abort
> should been used instead.
>
> Thanks for the comment.
>

Looking more at it, I think we should keep period = 0 forbidden. So it's treated 
as undefined behaviour and ptimer user should take care of it. If we'd want to 
handle period = 0 within ptimer, then we should also handle freq = 0, which 
implies potential ptimer VMSD version bump. Also it is uncertain what default 
behaviour should be chosen for period = 0, my guess is that pausing 
(_not_disabling_) the timer (like in freq = 0 case) should be more common among 
various hardware. If you have any thoughts on it, please let me know.

-- 
Dmitry