Re: [PATCH v2 1/4] PM / Domains: Remove pm_genpd_dev_need_restore() API

From: Ulf Hansson <ulf.hansson@linaro.org>
To: Sylwester Nawrocki <s.nawrocki@samsung.com>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Len Brown <len.brown@intel.com>, Pavel Machek <pavel@ucw.cz>,
	"linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	linux-samsung-soc <linux-samsung-soc@vger.kernel.org>,
	Geert Uytterhoeven <geert+renesas@glider.be>,
	Kevin Hilman <khilman@linaro.org>,
	Alan Stern <stern@rowland.harvard.edu>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Tomasz Figa <tomasz.figa@gmail.com>,
	Simon Horman <horms@verge.net.au>,
	Magnus Damm <magnus.damm@gmail.com>,
	Ben Dooks <ben-linux@fluff.org>,
	Kukjin Kim <kgene.kim@samsung.com>,
	Philipp Zabel <philipp.zabel@gmail.com>,
	Mark Brown <broonie@kernel.org>, Wolfram Sang <wsa@the-dreams.de>,
	Russell King <linux@arm.linux.org.uk>,
	Dmitry Torokhov <dmitry.torokhov@gmail.com>,
	Jack Dai <jack.dai@rock-chips.com>,
	Jinkun
Subject: Re: [PATCH v2 1/4] PM / Domains: Remove pm_genpd_dev_need_restore() API
Date: Fri, 3 Oct 2014 12:36:43 +0200	[thread overview]
Message-ID: <CAPDyKFqi=eKYBXSuRPzTZ0vybRfV6oMNt-_vCqT-6+otGiMucQ@mail.gmail.com> (raw)
In-Reply-To: <542D7525.8000804@samsung.com>

On 2 October 2014 17:54, Sylwester Nawrocki <s.nawrocki@samsung.com> wrote:
> On 02/10/14 15:30, Ulf Hansson wrote:
> [...]
>> Correct me if I am wrong, but I think in principle these exynos
>> drivers don't use pm_runtime_set_active() during ->probe() and are
>> instead relying on CONFIG_PM_RUNTIME to be enabled.
>
> Yes, pm_runtime_set_active() is not used in probe(), I believe this
> is not required. In case of those IP blocks there is no use of activating
> them during probe(). Instead we check if PM_RUNTIME is enabled through
> pm_runtime_enabled() helper and enable the device clock(s) if not.
> I agree it all doesn't quite work in current mainline for !PM_RUNTIME,
> since there is nothing ensuring that the power domains are enabled
> in such kernel configuration.
>
>> That's not a good behaviour. If these drivers are build without
>> CONFIG_PM_RUNTIME - they won't work.
>
> They wouldn't similarly work with pm_runtime_set_active() call in probe()
> with CONFIG_PM_RUNTIME disabled, would they ?

Yes they would, although they require some minor additional adaptations.

Those resources that are enabled from the driver's runtime PM resume
callback, should also be enabled during ->probe(). The
pm_runtime_set_active() will then update the state to reflect this.

Then, if CONFIG_PM_RUNTIME is enabled - the device will be scheduled
to go inactive from driver core (pm_request_idle()), after ->probe()
has completed. Thus saving power if it's unused.
If CONFIG_PM_RUNTIME isn't enabled - the driver will still be
functional, since all resources are enabled during ->probe().

Kind regards
Uffe