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

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Message-ID: <03e7f4d0-0c1b-edbb-3e24-83faf4b3a12b@nvidia.com>
Date:   Wed, 15 Mar 2017 08:57:56 +0000
From:   Jon Hunter <jonathanh@...dia.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
CC:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Kevin Hilman <khilman@...nel.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Stanimir Varbanov <stanimir.varbanov@...aro.org>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Linux PM list <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>
Subject: Re: [RFC PATCH 0/3] PM / Domains: Add support for devices that
 require multiple domains


On 13/03/17 14:42, Ulf Hansson wrote:
> On 13 March 2017 at 15:09, Jon Hunter <jonathanh@...dia.com> wrote:
>> Hi Ulf,
>>
>> On 13/03/17 11:45, Ulf Hansson wrote:
>>> +Björn
>>>
>>> On 13 March 2017 at 10:37, Jon Hunter <jonathanh@...dia.com> 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 Björn, 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.

No problem. I should point out the above is for the #power-domain-cells
= <0> case.

>>
>> 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.

OK, fair enough. Any in particular you are concerned about?

> 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!?

Right that is a concern, however, I think that in the long-term we would
be better off with the power-domains being controlled by the same
underlying code as opposed to something different.

Cheers
Jon

-- 
nvpublic