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

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Message-ID: <3e88692d-613b-9c25-2554-7d399c45637a@nvidia.com>
Date:   Mon, 13 Mar 2017 14:09:34 +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

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>;
	};

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?

Cheers
Jon

-- 
nvpublic