Re: [RFC PATCH 0/3] PM / Domains: Add support for devices that require multiple domains

[Ulf Hansson]

On 13 March 2017 at 15:09, Jon Hunter <jonathanh@xxxxxxxxxx> wrote:
> Hi Ulf,
>
> On 13/03/17 11:45, Ulf Hansson wrote:
>> +BjÃrn
>>
>> On 13 March 2017 at 10:37, Jon Hunter <jonathanh@xxxxxxxxxx> wrote:
>>> Hi Rafael, Kevin, Ulf,
>>>
>>> Looks like there is still some interest/needs in/for this. Any thoughts
>>> on how we can move this forward?
>>
>> At the Linaro Connect last week, I was talking to BjÃrn, Rajendra and
>> Stephen more about these related issues.
>>
>> It definitely seems like we need to progress with this somehow,
>> meaning we need a solution for being able to associate a device with
>> more than one PM domain. In that context, I don't think genpd based on
>> its current design, is a good fit to solve the problem.
>>
>> Instead I think we need something entirely new (perhaps some code can
>> be borrowed from genpd), which is more similar to the clock/regulator
>> framework. In other words, what you also were suggesting in a earlier
>> reply.
>> In this way, the driver/subsystem gains full flexibility of managing
>> its device's PM domains, which seems like the best future-proof
>> solution.
>
> I agree, I think that that would give us the most flexibility to handle
> whatever scenario. However, I was thinking that we could still use the
> genpd core to register pm-domains with and control. My thought was to
> allow devices to have a bindings with multiple pm-domains ...
>
>         dev-xyz {
>                 ...
>                 power-domains = <&domain-a>, <&domain-b>;
>         };

This could work. However, let's involve DT maintainers to make sure we
get their input to this. Perhaps they prefer a different approach.

>
> Then in the genpd core we do having something like ...
>
> diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
> index e697dec9d25b..d1ae6ddf4903 100644
> --- a/drivers/base/power/domain.c
> +++ b/drivers/base/power/domain.c
> @@ -2026,6 +2026,15 @@ int genpd_dev_pm_attach(struct device *dev)
>                                                 "samsung,power-domain", 0);
>                 if (!pd_args.np)
>                         return -ENOENT;
> +       } else if (ret > 1) {
> +               /*
> +                * If there are more than one PM domain defined for a device,
> +                * then these need to be manually controlled by the device
> +                * driver because the genpd core cannot bind a device with
> +                * more than one PM domain.
> +                */
> +               dev_dbg(dev, "cannot add PM domains, %d detected!\n", ret);
> +               return 0;
>         }
>
> Then add some new public APIs for getting and controlling the pm-domains ...
>
> struct generic_pm_domain *pm_genpd_get(struct device *dev, char *name);
> - Use 'dev->of_node' to look-up pm-domain if populated, else uses name.
>
> struct generic_pm_domain *of_pm_genpd_get(struct device *dev, int index);
> void pm_genpd_put(struct generic_pm_domain *pd);
> int pm_genpd_power_on(struct generic_pm_domain *pd);
> int pm_genpd_power_off(struct generic_pm_domain *pd);
> - Power on/off APIs would be synchronous types
>
> Are there any potential pitfalls of the above?

So if I understand correctly, you would like to extend genpd with some
new APIs. It's worth a try, however my main worries are these:

1) These new API must not be allowed to be abused.
I have seen that before as when people try to handle some corner
cases, I don't want to that to happen again. To avoid that, perhaps we
should continue the re-structuring and thus move structures/datas that
are currently public, to be internal to genpd. To get a clean
interface.

2) I wouldn't be surprised if we run into some tricky corner cases, as
we get a mixture of devices handled by runtime PM and in some other
cases via new APIs. Perhaps that can be sorted out!?

Kind regards
Uffe