linux-kernel - Re: [PATCH v5 5/6] mfd: dt-bindings: add device tree bindings for Hi3519 sysctrl

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Message-ID: <20160125142609.GR3368@x1>
Date:	Mon, 25 Jan 2016 14:26:09 +0000
From:	Lee Jones <lee.jones@...aro.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	xuejiancheng <xuejiancheng@...wei.com>, mturquette@...libre.com,
	sboyd@...eaurora.org, p.zabel@...gutronix.de, robh+dt@...nel.org,
	pawel.moll@....com, mark.rutland@....com,
	ijc+devicetree@...lion.org.uk, galak@...eaurora.org,
	linux@....linux.org.uk, khilman@...aro.org, olof@...om.net,
	xuwei5@...ilicon.com, haojian.zhuang@...aro.org,
	zhangfei.gao@...aro.org, bintian.wang@...wei.com,
	linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org,
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	yanhaifeng@...ilicon.com, yanghongwei@...ilicon.com,
	suwenping@...ilicon.com, ml.yang@...ilicon.com,
	gaofei@...ilicon.com, zhangzhenxing@...ilicon.com,
	xuejiancheng@...ilicon.com
Subject: Re: [PATCH v5 5/6] mfd: dt-bindings: add device tree bindings for
 Hi3519 sysctrl

On Tue, 12 Jan 2016, Arnd Bergmann wrote:

> On Tuesday 12 January 2016 17:28:05 xuejiancheng wrote:
> > >>>>>
> > >>>> Not yet.
> > >>>> Arnd Bergmann and Rob Herring all suggested adding a specific compatible string
> > >>>> with the SOC name. This binding is just used for describing the compatible string now.
> > >>>> When more functions on hi3519 SOC are added later, the specific driver will be also
> > >>>> needed.
> > >>>
> > >>> Save this binding until it has more functionality.  We here "I'll add
> > >>> to this later" all too often.
> > >>>
> > >>
> > >> In the hi3519.dtsi file, there is a system-controller device node described like below:
> > >> sysctrl: system-controller@...10000 {
> > >>      compatible = "hisilicon,hi3519-sysctrl", "syscon";
> > >>      reg = <0x12010000 0x1000>;
> > >> };
> > >> Do you mean that I should remove "hisilicon,hi3519-sysctrl" and just use "syscon" as the
> > >> compatible string?　
> > > 
> > > Where is this compatible string _used_?
> > > 
> > >> If I want to add "hisilicon,hi3519-sysctrl" for hi3519. where should I put this binding?
> > >> Could you give some suggestions?  Thank you very much!
> > > 
> > > If you're not using the compatible i.e. the device doesn't have its
> > > own driver yet, then there is no need to supply the binding at all, is
> > > there?
> > > 
> > 
> > OK. Thank you.
> > 
> 
> Sorry for stepping in late here. I still think that every syscon device should
> come with a specific compatible string, so we have the option of creating a
> driver later on, and I'd like to see a binding document that lists those strings
> (which I believe exists here).
> 
> It's really hard to add compatible strings later on, anything else we can
> work around by keying off that string and adding a workaround in the kernel.

Why is it more difficult (or any different) to add a compatible string
later (when it is used) over now (when it is not used)?

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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