linux-kernel - Re: [PATCH RFC 04/10] base: power: Add generic OF-based power domain look-up

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Message-ID: <20140122110018.GB24288@e102568-lin.cambridge.arm.com>
Date:	Wed, 22 Jan 2014 11:00:18 +0000
From:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:	Tomasz Figa <t.figa@...sung.com>
Cc:	Tomasz Figa <tomasz.figa@...il.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
	Russell King <linux@....linux.org.uk>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Kumar Gala <galak@...eaurora.org>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Mark Rutland <Mark.Rutland@....com>,
	Pawel Moll <Pawel.Moll@....com>,
	Rob Herring <robh+dt@...nel.org>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Stephen Warren <swarren@...dotorg.org>
Subject: Re: [PATCH RFC 04/10] base: power: Add generic OF-based power domain
 look-up

On Mon, Jan 20, 2014 at 05:32:53PM +0000, Tomasz Figa wrote:
> Hi Lorenzo,
> 
> On 16.01.2014 17:34, Lorenzo Pieralisi wrote:
> > Hi Tomasz,
> >
> > thank you for posting this series. I would like to use the DT bindings
> > for power domains in the bindings for C-states on ARM:
> >
> > http://comments.gmane.org/gmane.linux.power-management.general/41012
> >
> > and in particular link a given C-state to a given power domain so that the
> > kernel will have a way to actually check what devices are lost upon C-state
> > entry (and for devices I also mean CPU peripheral like PMUs, GIC CPU IF,
> > caches and possibly cpus, all of them already represented with DT nodes).
> >
> > I have a remark:
> >
> > -  Can we group device nodes under a single power-domain-parent so that
> >     all devices defined under that parent won't have to re-define a
> >     power-domain property (a property like interrupt-parent, so to speak)
> >
> > What do you think ?
> 
> Hmm, I can see potential benefits of such construct on platforms with 
> clear hierarchy of devices, but to make sure I'm getting it correctly, 
> is the following what you have in mind?
> 
> soc-domain-x@...40000 {
> 	compatible = "...";
> 	reg = <...>;
> 	power-domain-parent = <&power_domains DOMAIN_X>;
> 
> 	device@...0 {
> 		compatible = "...";
> 		// inherits power-domain = <&power_domains DOMAIN_X>
> 	};
> 
> 	device@...0 {
> 		compatible = "...";
> 		// inherits power-domain = <&power_domains DOMAIN_X>
> 	};
> };

Yes, exactly, it could avoid duplicated data. I still have an issue
with nodes that are per-cpu but define just one node (eg PMU), since
a CPU might belong in a power-domain on its own (ie one power domain
per-CPU) and basically this means that arch-timers, PMU & company should
link to multiple power domains, ie one per CPU or we find a way to define
a power domain as "banked".

I need to think about this a bit more, thanks for your feedback.

Lorenzo

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