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

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Date:	Mon, 01 Sep 2014 19:05:51 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Lee Jones <lee.jones@...aro.org>
Cc:	linux-arm-kernel@...ts.infradead.org, kgene.kim@...sung.com,
	linux@....linux.org.uk, naushad@...sung.com,
	Pankaj Dubey <pankaj.dubey@...sung.com>,
	Tomasz Figa <t.figa@...sung.com>, linux-kernel@...r.kernel.org,
	joshi@...sung.com, linux-samsung-soc@...r.kernel.org,
	broonie@...nel.org, thomas.ab@...sung.com,
	vikas.sajjan@...sung.com, chow.kim@...sung.com
Subject: Re: [PATCH] mfd: syscon: Decouple syscon interface from syscon devices

On Monday 01 September 2014 17:04:26 Lee Jones wrote:
> On Mon, 01 Sep 2014, Arnd Bergmann wrote:
> > Maybe I'm misreading the patch, but I don't see how it creates a
> > migration path. What I want to end up with is infrastructure that
> > lets anybody call syscon_regmap_lookup_by_pdevname or
> > syscon_regmap_lookup_by_compatible (if they really need to)
> > without needing the platform_driver for syscon. That should not
> > require any form of compatibility layer because to the driver
> > using it there is no API change.
> 
> Somehow I think the likelyhood is that I am misreading the patch.
> 
> I thought that before this patch drivers we had to register a syscon
> device to bind to this driver, which was fine for the first use-cases
> of syscon as it wasn't required too early during boot.  However, now
> there are use-cases where systems require access to syscon registers
> eariler in boot we require a means to obtain access prior to device
> probing.  I thought this patch not only provides that possibilty, but
> also leaves in the ability to register direct from DT.

Right, it does provide the ability to have syscon before devices
are registered, I missed that part.

> > In contrast, this patch introduces a new of_syscon_{un,}register()
> > interface that would get removed after the the above has
> > been implemented, causing extra churn for any driver that also
> > wants to provide a regmap-like interface.
> 
> When will we ever not have to register syscon?

The idea is that we implicitly register the syscon block when someone
calls syscon_regmap_lookup_by_compatible or syscon_regmap_lookup_by_phandle
and then return a reference to that new syscon. When another driver
looks up the same device node, we just pass a reference to the existing
syscon.

	Arnd
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