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

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Date:	Tue, 18 Jun 2013 17:02:49 +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 1:36 PM, Russell King - ARM Linux
<linux@....linux.org.uk> wrote:

> Maybe what we need is something like this:
>
> static DEFINE_SPINLOCK(io_lock);
> static void modifyl(u32 new, u32 mask, void __iomem *reg)
> {
>         unsigned long flags;
>         u32 val;
>
>         spin_lock_irqsave(&io_lock, flags);
>         val = readl(reg) & ~mask;
>         val |= new | mask;
>         writel(val, reg);
>         spin_unlock_irqrestore(&io_lock, flags);
> }
>
> in order to provide arbitrated access to these kinds of multifunction
> registers in a safe, platform agnostic way.

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)

Yours,
Linus Walleij
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