linux-kernel - Re: [RFC][PATCH v3 1/3] runtime interpreted power sequences

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Message-ID: <20120802084541.GA15042@avionic-0098.adnet.avionic-design.de>
Date:	Thu, 2 Aug 2012 10:45:41 +0200
From:	Thierry Reding <thierry.reding@...onic-design.de>
To:	Alex Courbot <acourbot@...dia.com>
Cc:	Stephen Warren <swarren@...dotorg.org>,
	Stephen Warren <swarren@...dia.com>,
	Simon Glass <sjg@...omium.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>
Subject: Re: [RFC][PATCH v3 1/3] runtime interpreted power sequences

On Thu, Aug 02, 2012 at 05:27:44PM +0900, Alex Courbot wrote:
> On Thu 02 Aug 2012 05:21:57 PM JST, Thierry Reding wrote:
> >* PGP Signed by an unknown key
> >
> >On Thu, Aug 02, 2012 at 05:00:13PM +0900, Alex Courbot wrote:
> >>On 07/31/2012 07:45 AM, Stephen Warren wrote:
> >>>Oh I see. That's a little confusing. Why not just reference the relevant
> >>>resources directly in each step; something more like:
> >>>
> >>>		gpio@1 {
> >>>			action = "enable-gpio";
> >>>			gpio = <&gpio 1 0>;
> >>>		};
> >>>
> >>>I guess that might make parsing/building a little harder, since you'd
> >>>have to detect when you'd already done gpio_request() on a given GPIO
> >>>and not repeat it or something like that, but to me this makes the DT a
> >>>lot easier to comprehend.
> >>
> >>I tried to move towards having the phandles directly in the
> >>sequences themselves - that reminded me why I did not do that in the
> >>first place. Let's say we have a sequence like this (reg property
> >>omitted on purpose):
> >>
> >>	power-on-sequence {
> >>		step@0 {
> >>			regulator = <&backlight_reg>;
> >>			enable;
> >>		};
> >>		step@1 {
> >>			delay = <10000>;
> >>		};
> >>		step@2 {
> >>			pwm = <&pwm 2 5000000>;
> >>			enable;
> >>		};
> >>		step@3 {
> >>			gpio = <&gpio 28 0>;
> >>			enable;
> >>		};
> >>	};
> >>
> >>The problem is, how do we turn these phandles into the resource of
> >>interest. The type of the resource can be infered by the name of the
> >>property. The hard part is resolving the resource from the phandle -
> >>it seems like the API just does not allow to do this. GPIO has
> >>of_get_named_gpio, but AFAIK there are no equivalent for regulator
> >>consumer and PWM: the only way to use the DT with them is through
> >>get_regulator and get_pwm which work at the device level.
> >>
> >>Or is there a way that I overlooked?
> >
> >No, you are right. Perhaps we should add exported functions that do the
> >equivalent of of_pwm_request() or the regulator_dev_lookup() and
> >of_get_regulator() pair.
> 
> How would that be looked with respect to "good DT practices"? I can
> somehow understand the wish to restrain DT access to these functions
> that integrate well with current workflows. Aren't we going to be
> frowned upon if we make more low-level functions public?

Yes, I think that's exactly what will happen.

Thierry

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