From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Rafael J. Wysocki" <rjw-KKrjLPT3xs0@public.gmane.org>
Subject: Re: [PATCH RESEND] i2c/nomadik: runtime PM support
Date: Thu, 3 May 2012 21:25:37 +0200
Message-ID: <201205032125.37631.rjw@sisk.pl>
References: <1331213407-10135-1-git-send-email-linus.walleij@stericsson.com> <201205031459.25262.rjw@sisk.pl> <20120503133907.GG3955@opensource.wolfsonmicro.com>
Mime-Version: 1.0
Content-Type: Text/Plain;
  charset="iso-8859-2"
Content-Transfer-Encoding: 7bit
Return-path: <linux-i2c-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
In-Reply-To: <20120503133907.GG3955-yzvPICuk2AATkU/dhu1WVueM+bqZidxxQQ4Iyu8u01E@public.gmane.org>
Sender: linux-i2c-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
To: Mark Brown <broonie-yzvPICuk2AATkU/dhu1WVueM+bqZidxxQQ4Iyu8u01E@public.gmane.org>
Cc: Linus Walleij <linus.walleij-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>, Magnus Damm <magnus.damm-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Wolfram Sang <w.sang-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>, Ben Dooks <ben-i2c-elnMNo+KYs3YtjvyW6yDsg@public.gmane.org>, linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Jonas Aaberg <jonas.aberg-0IS4wlFg1OjSUeElwK9/Pw@public.gmane.org>, Rickard ANDERSSON <rickard.andersson-0IS4wlFg1OjSUeElwK9/Pw@public.gmane.org>, Rabin VINCENT <rabin.vincent-0IS4wlFg1OjSUeElwK9/Pw@public.gmane.org>
List-Id: linux-i2c@vger.kernel.org

On Thursday, May 03, 2012, Mark Brown wrote:
> On Thu, May 03, 2012 at 02:59:25PM +0200, Rafael J. Wysocki wrote:
> > On Thursday, May 03, 2012, Linus Walleij wrote:
> 
> > > If *all* runtime_resume() hooks for *all* devices in the same power
> > > domain are called at this time on the way up/down we get a major
> > > overhead as our primary power domain is pretty big.
> 
> > FWIW, in the generic PM domains framework used on the sh7372 platform we have
> > a need_restore flag whose meaning is whether or not to call .runtime_suspend()
> > (or its domain-specific counterpart) when the domain is about to be powered
> > off and .runtime_resume() when the device is resumed by the runtime PM
> > framework.  Those two callbacks are meant to save and restore the device's
> > state, respectively, and there are two more domain-specific callbacks,
> > .stop() and .start() that (in the case of sh7372) manipiulate the devices'
> > clocks.
> 
> > So, if pm_runtime_suspend() is called for a device, we first check if it's OK
> > to call .stop() for it (according to PM QoS constraints), but we don't call
> > .runtime_suspend() for it yet at this point.  Next, we check if it's OK to
> > power off the domain containing the device (taking PM QoS constraints and
> > subdomains into consideration) and if we decide to do that, we call
> > .runtime_suspend() for the devices in the domain, but only those whose
> > need_restore flags are unset.  Then, if pm_runtime_resume() is called for
> > one of the devices, we check its need_restore flag and call .runtime_resume()
> > for the device if the flag set and .start() is called subsequently.
> 
> This seems like a really useful idiom in general - might it be worth
> supporting as a standard framework feature?

The generic PM domains framework does this, it's not platform-specific
(if I understood your question correctly).

Thanks,
Rafael