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

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Date:	Tue, 02 Sep 2014 14:02:48 +0530
From:	Pankaj Dubey <pankaj.dubey@...sung.com>
To:	'Arnd Bergmann' <arnd@...db.de>,
	linux-arm-kernel@...ts.infradead.org
Cc:	'Lee Jones' <lee.jones@...aro.org>, kgene.kim@...sung.com,
	linux@....linux.org.uk, naushad@...sung.com,
	'Tomasz Figa' <t.figa@...sung.com>,
	linux-kernel@...r.kernel.org, joshi@...sung.com,
	vikas.sajjan@...sung.com, linux-samsung-soc@...r.kernel.org,
	broonie@...nel.org, thomas.ab@...sung.com, chow.kim@...sung.com
Subject: RE: [PATCH] mfd: syscon: Decouple syscon interface from syscon devices



> -----Original Message-----
> From: Arnd Bergmann [mailto:arnd@...db.de]
> Sent: Tuesday, September 02, 2014 1:45 PM
> To: linux-arm-kernel@...ts.infradead.org
> Cc: Lee Jones; kgene.kim@...sung.com; linux@....linux.org.uk;
> naushad@...sung.com; Pankaj Dubey; Tomasz Figa;
linux-kernel@...r.kernel.org;
> joshi@...sung.com; vikas.sajjan@...sung.com; linux-samsung-
> soc@...r.kernel.org; broonie@...nel.org; thomas.ab@...sung.com;
> chow.kim@...sung.com
> Subject: Re: [PATCH] mfd: syscon: Decouple syscon interface from syscon
devices
> 
> On Tuesday 02 September 2014 09:05:16 Lee Jones wrote:
> > On Mon, 01 Sep 2014, Arnd Bergmann wrote:
> >
> > > 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.
> >
> > Doesn't sound too unreasonable.  So how about instead of exporting
> > these new of_syscon_{un,}register() calls, we make them static and
> > call them from syscon_regmap_lookup_by_{phandle,compatible}?
> 
> Yes, that would be a good start. We should think about whether we want to
remove
> the existing DT probing at the same time, since it becomes unused, and we
might
> want to move the code to drivers/base/regmap_*.c at some point.
> 


OK, I am working on these two parts. Once code is in proper form and tested
on
our setup I will post here.

Thanks,
Pankaj

> 	Arnd

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