linux-kernel - Re: [PATCH] mfd: syscon: Decouple syscon interface from syscon devices

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Message-ID: <20140901112549.GM7374@lee--X1>
Date:	Mon, 1 Sep 2014 12:25:49 +0100
From:	Lee Jones <lee.jones@...aro.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Pankaj Dubey <pankaj.dubey@...sung.com>,
	linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
	kgene.kim@...sung.com, linux@....linux.org.uk,
	vikas.sajjan@...sung.com, joshi@...sung.com, naushad@...sung.com,
	thomas.ab@...sung.com, chow.kim@...sung.com,
	Tomasz Figa <t.figa@...sung.com>, broonie@...nel.org
Subject: Re: [PATCH] mfd: syscon: Decouple syscon interface from syscon
 devices

On Mon, 01 Sep 2014, Arnd Bergmann wrote:
> On Monday 01 September 2014 08:49:18 Lee Jones wrote:
> > On Fri, 22 Aug 2014, Pankaj Dubey wrote:
> > 
> > > From: Tomasz Figa <t.figa@...sung.com>
> > > 
> > > Currently a syscon entity can be only registered directly through a
> > > platform device that binds to a dedicated driver. However in certain use
> > > cases it is desirable to make a device used with another driver a syscon
> > > interface provider. For example, certain SoCs (e.g. Exynos) contain
> > > system controller blocks which perform various functions such as power
> > > domain control, CPU power management, low power mode control, but in
> > > addition contain certain IP integration glue, such as various signal
> > > masks, coprocessor power control, etc. In such case, there is a need to
> > > have a dedicated driver for such system controller but also share
> > > registers with other drivers. The latter is where the syscon interface
> > > is helpful.
> > > 
> > > This patch decouples syscon object from syscon driver, so that it can be
> > > registered from any driver in addition to the original "syscon" platform
> > > driver.
> > > 
> > > Signed-off-by: Tomasz Figa <t.figa@...sung.com>
> > > Signed-off-by: Pankaj Dubey <pankaj.dubey@...sung.com>
> > > ---
> > > 
> > > RFC patch [1] was posted by Tomasz Figa. This patch addresses some of
> > > comments given by Arnd to RFC patch, and further decouples syscon from
> > > device model. It also gives flexibility of registering with syscon at
> > > early stage using device_node object.
> > 
> > It would be helpful if Arnd gave this revision his blessing (Ack).
> 
> I never saw a reason why we don't take this all the way as discussed
> a few times: Completely remove the dependency of syscon on having
> a platform driver for it, and make it possible to just call
> syscon_regmap_lookup_by_phandle() without having to register
> it first.

I think this sounds like a good end-state.  Migrating over by
supporting both methods in this way does sound like the correct thing
to do though.  Doing so is likely to dramatically reduce the effect on
current users.

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog
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