linux-kernel - Re: [PATCH v8 4/9] mfd: Add binding document for NVIDIA Tegra XUSB

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Date:	Thu, 21 May 2015 09:19:00 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Thierry Reding <thierry.reding@...il.com>
Cc:	Lee Jones <lee.jones@...aro.org>,
	Andrew Bresticker <abrestic@...omium.org>,
	Jon Hunter <jonathanh@...dia.com>,
	Stephen Warren <swarren@...dotorg.org>,
	Alexandre Courbot <gnurou@...il.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Samuel Ortiz <sameo@...ux.intel.com>
Subject: Re: [PATCH v8 4/9] mfd: Add binding document for NVIDIA Tegra XUSB

On Wed, May 20, 2015 at 4:52 PM, Thierry Reding
<thierry.reding@...il.com> wrote:

> I'm a little confused by the simple-mfd approach. The only code I see in
> linux-next for this is a single line that adds the "simple-mfd" string
> to the OF device ID table in drivers/of/platform.c. As far as I can tell
> this will merely cause child devices to be created. There won't be a
> shared regmap and resources won't be set up properly either.

That is correct. The simple-mfd is a two-component approach.

Ideally, in the simplest case, you combine simple-mfd with syscon.

foo@0 {
    compatible = "foo", "syscon", "simple-mfd";
    reg = <0x10000000 0x1000>;

    bar@1 {
        compatible = "bar";
    };

    baz@2 {
        compatible = "baz";
    };
};

This will instantiate bar and baz.

These subdrivers then probe and:

probe() {
   struct regmap *map;

   map = syscon_node_to_regmap(parent->of_node);
   (...)
}

Simple, syscon is the MFD hub.

Yours,
Linus Walleij
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