linux-kernel - Re: [PATCH v4 02/10] pinctrl: mvebu: dove pinctrl driver

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Message-ID: <CACRpkdadS4Si0pqrxRrnriQk81aZgeKKQta7onEpJv3vi6mfdw@mail.gmail.com>
Date:	Tue, 18 Jun 2013 17:23:00 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Rob Landley <rob@...dley.net>,
	Lior Amsalem <alior@...vell.com>, Andrew Lunn <andrew@...n.ch>,
	Jason Cooper <jason@...edaemon.net>,
	Gregory CLEMENT <gregory.clement@...e-electrons.com>,
	Ben Dooks <ben.dooks@...ethink.co.uk>,
	Stephen Warren <swarren@...dotorg.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v4 02/10] pinctrl: mvebu: dove pinctrl driver

On Tue, Jun 18, 2013 at 5:11 PM, Russell King - ARM Linux
<linux@....linux.org.uk> wrote:
> On Tue, Jun 18, 2013 at 05:02:49PM +0200, Linus Walleij wrote:
>> Nowadays I would do the above with regmap_update_bits().
>>
>> Mutual exclusion for read-modify-write of individual bits in a
>> register is one of those cases where doing a regmap over
>> a memory-mapped register range makes a lot of sense.
>> (drivers/mfd/syscon.c being a nice example)
>
> So, for that solution we need to have some kind of global regmap per
> register or somesuch.  Then you run into regmap needing a struct
> device - well, with a shared register, which struct device do you
> use, or do you have to invent one?

Usually, like for syscon, you create an MFD hub which
carry the regmap.

> That sounds more heavy-weight than is really necessary.

May be so, especially if there is just one register to protect.
The usefulness of MM-regmap increase with the set of registers
needing to be protected.

Yours,
Linus Walleij
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