Re: [PATCH V5 11/14] soc: tegra: pmc: Add generic PM domain support

[Jon Hunter <jonathanh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>]

On 11/02/16 09:57, Ulf Hansson wrote:
> On 11 February 2016 at 10:13, Jon Hunter <jonathanh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org> wrote:
>>
>> On 10/02/16 18:25, Ulf Hansson wrote:
>>
>> [snip]
>>
>>>>> Perhaps there's a way to allow the generic PM domain to control this
>>>>> by itself. If we for example used the struct device corresponding to
>>>>> the powergate driver, genpd could use it to distinguish between
>>>>> various instances of genpd structs..!? Maybe it would simplify the way
>>>>> to deal with removing domains?
>>>>
>>>> Yes, that would be ideal. However, would have require changing
>>>> genpd_init()? I am not sure how genpd would be able to access the device
>>>> struct for the powergate driver because we don't provide this via any
>>>> API I am aware of? And I am guessing that you don't wish to expose the
>>>> gpd_list to the world either.
>>>>
>>>> If there is an easy way, I am open to it, but looking at it today, I am
>>>> not sure I see a simple way in which we could add a new API to do this.
>>>> However, may be I am missing something!
>>>
>>> If we add a new __pm_genpd_init() API, that could require a struct
>>> device to be provided. That API will thus invoke the existing
>>> pm_genpd_init() but also deal with the extra things needed here.
>>>
>>> I would also allow such an API to return an error code.
>>>
>>> Correspondingly, pm_genpd_remove() could be required to be provided
>>> with a struct device.
>>>
>>> Existing users of pm_genpd_init() can then convert to
>>> __pm_genpd_init() whenever suitable.
>>>
>>> Of course, another option is just to add new member in the genpd
>>> struct for the struct *device. The caller of pm_genpd_init() could
>>> check it, but allow it to be NULL. Although, the pm_genpd_remove() API
>>> would require that pointer to the struct device to be set...
>>>
>>> What do you think?
>>
>> Yes, sounds good. May be it is simpler just to add a new member and let
>> the platform genpd driver handle it.
>>
>> I am wondering if in addition to pm_genpd_remove(), we then just have a
>> function called pm_genpd_remove_tail(), which allows you to pass the
>> struct device pointer and will remove the last pm-domain from the
>> gpd_list and return the genpd pointer if successful. Internally, it will
>> call pm_genpd_remove(). It seems to me that if there are nested
>> pm-domains, then we probably want to remove them starting from the tail
>> as opposed to the head.
>>
>> How does that sound?
> 
> Why not make pm_genpd_remove() to behave as you describe for
> pm_genpd_remove_tail()?
> That's probably the only sane way to remove genpds anyhow!?

Simply to offer flexibility. I could see that for some devices that have
no dependencies between pm-domains and have a static list of pm-domains,
they can simply call pm_genpd_remove() for a given pm-domain. However,
that said, I can envision a case where a single pm-domain would be
removed by itself and so may be there is no benefit?

Cheers
Jon