Re: [PATCHv2 04/19] ARM: OMAP4: PM: save/restore all DPLL settings in OFF mode

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On Thu, May 31, 2012 at 3:39 AM, Kevin Hilman <khilman@xxxxxx> wrote:
> "Menon, Nishanth" <nm@xxxxxx> writes:
>
>> On Wed, May 30, 2012 at 12:59 PM, Kevin Hilman <khilman@xxxxxx> wrote:
>>> "Menon, Nishanth" <nm@xxxxxx> writes:
>>>
>>>> On Thu, May 17, 2012 at 3:52 AM, Shilimkar, Santosh
>>>> <santosh.shilimkar@xxxxxx> wrote:
>>>>> On Thu, May 17, 2012 at 12:34 PM, Shilimkar, Santosh
>>>>> <santosh.shilimkar@xxxxxx> wrote:
>>>>>> On Thu, May 17, 2012 at 4:12 AM, Kevin Hilman <khilman@xxxxxx> wrote:
>>>>>>> Tero Kristo <t-kristo@xxxxxx> writes:
>>>>>>>
>>>> [...]
>>>>>>> - Rather than hooking into omap4_enter_lowpower(), should use
>>>>>>>  the cluster PM enter/exit notifier chain.
>>>>>>>
>>>>>> This is again specific to device OFF only and not related to CPU
>>>>>> cluster state as such. So I don't think notifiers should be used here.
>>>>>>
>>>>>> O.w even when we attempt just MPU OSWR C-state, all these functions will
>>>>>> get called in notifier chain.
>>>>>>
>>>>> Just a thought, we can have a separate notifier chain for device OFF. It can
>>>>> allow use to get rid of 'enable_off_mode" kind of flags and can be
>>>>> used by many drivers too.
>>>>
>>>> Like the overall idea, but one minor dumb concern might be sequencing
>>>> of notifiers
>>>>  - OFF entry and restore needs things to be executed in a specific sequence.
>>>> How do we plan to ensure the sequence is maintained in a notifier call
>>>> chain? one
>>>> possible option might be a "priority" based scheme?
>>>
>>> Or just combine the events that need a specific sequence into single
>>> notifier callback function.
>> There is other issues in case of failure cases -> abort of OFF
>> sequence due to pending interrupt
>> detected as part of a notifier - error handling needs to be sane in
>> proper sequence.
>> I understand and appreciate the intent of replacing the single mega
>> enter_sleep with a chain of notifiers
>> but any such option will need to be scalable enough to handle weird
>> erratum handling (HSI CAWAKE as an example)
>> which potentially break the logic flow and be either be equal or
>> better than what we have today interms of
>> error handling. since these notifiers will be triggered for
>> CPUIDLE(performance sensitive) and suspend, the intricacies
>> might be better understood by seeing how this proposed notifiers look like.
>
> Makes sense.  Thanks for clarifying.
>
> What $SUBJECT series proposed was indeed a "mega function", but one that
> was just a list of function calls with no error checking or recovery,
> and no documentation/description about dependencies/sequencing etc. etc.
> Based on the patches at hadn (which is all reviewers have to go on),
> notifiers seemed to be a good fit.
>
> If there are good reasons that all of the device-off events need to be
> coordinated/synchronized/sequenced (and it sounds like there are, thanks
> for pointing them out), I am not opposed to that approach.  It simply
> needs to be well described in the changlog.
>
There are sequence dependencies but lot of code can be extracted and put
into smaller blocks that is independent.

I agree for the error handling part notifier chain could be an issue.

Regards
Santosh

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