linux-kernel - Re: [RFC v4 01/14] regulator: of: Add helper for getting all supplies

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Date:	Fri, 10 Jun 2016 12:30:56 -0500
From:	Rob Herring <robh@...nel.org>
To:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
Cc:	Mark Brown <broonie@...nel.org>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Sebastian Reichel <sre@...nel.org>,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Liam Girdwood <lgirdwood@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Hans de Goede <hdegoede@...hat.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	Heiko Stuebner <heiko@...ech.de>, linux-mmc@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-usb@...r.kernel.org, linux-fbdev@...r.kernel.org,
	hzpeterchen@...il.com,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [RFC v4 01/14] regulator: of: Add helper for getting all supplies

On Thu, Jun 09, 2016 at 01:42:02PM +0200, Krzysztof Kozlowski wrote:
> On 06/09/2016 12:29 PM, Mark Brown wrote:
> > On Thu, Jun 09, 2016 at 11:44:18AM +0200, Krzysztof Kozlowski wrote:
> >> Few drivers have a need of getting regulator supplies without knowing
> >> their names:
> >> 1. The Simple Framebuffer driver works on setup provided by bootloader
> >>    (outside of scope of kernel);
> >> 2. Generic power sequence driver may be attached to any device node.
> >>
> >> Add a Device Tree helper for parsing "-supply" properties and returning
> >> allocated bulk regulator consumers.
> > 
> > I'm still very concerned that this is just an invitation to people to
> > write half baked regulator consumers and half baked DTs to go along with
> > it, making it a standard API that doesn't have big red flags on it that
> > will flag up when "normal" drivers use it is not good.  Right now this
> > just looks like a standard API and people are going to just start using
> > it.  If we are going to do this perhaps we need a separate header or
> > something to help flag this up.
> 
> No problem, I can move it to a special header.  Actually, if you dislike
> this as an API, it does not have to be in header at all.  I can just
> duplicate the simplefb code.
> 
> > In the case of power sequences I'd expect the sequences to perform
> > operations on named supplies - the core shouldn't know what the supplies
> > are but the thing specifying the sequence should.
> 
> Hm, so maybe passing names like:
> 
> usb3503@08 {
> 	reset-gpios = <&gpx3 5 GPIO_ACTIVE_HIGH>;
> 	initial-mode = <1>;
> 	vdd-supply = <&buck8_reg>;
> 	foo-supply = <&buck9_reg>;
> 
>         power-sequence;
> 	power-sequence-supplies = "vdd", "foo";

This alone would be fine as it is just one property, but then what's 
next? power-sequence-delay, power-sequence-clocks, etc. What if you 
need to express ordering relationship of supplies, clocks, gpios? We end 
up with a scripting language in DT and we don't want to have that.

Rob