linux-kernel - Re: [PATCH 1/5 v2] MFD/OF: document MFD devices and handle simple-mfd

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Date:	Tue, 17 Mar 2015 15:27:23 +0000
From:	Lee Jones <lee.jones@...aro.org>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	Samuel Ortiz <sameo@...ux.intel.com>, linux-kernel@...r.kernel.org,
	Arnd Bergmann <arnd@...db.de>,
	Devicetree <devicetree@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Grant Likely <grant.likely@...aro.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>
Subject: Re: [PATCH 1/5 v2] MFD/OF: document MFD devices and handle simple-mfd

On Tue, 17 Mar 2015, Linus Walleij wrote:

> This defines a new compatible option for MFD devices "simple-mfd" that will
> make the OF core spawn child devices for all subnodes of that MFD device.
> It is optional but handy for things like syscon and possibly other
> simpler MFD devices.
> 
> Since there was no file to put the documentation in, I took this opportunity
> to make a small writeup on MFD devices and add the compatible definition
> there.
> 
> Suggested-by: Lee Jones <lee.jones@...aro.org>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Devicetree <devicetree@...r.kernel.org>
> Cc: Rob Herring <robh+dt@...nel.org>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Cc: Grant Likely <grant.likely@...aro.org>
> Cc: Pawel Moll <pawel.moll@....com>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Ian Campbell <ijc+devicetree@...lion.org.uk>
> Cc: Kumar Gala <galak@...eaurora.org>
> Signed-off-by: Linus Walleij <linus.walleij@...aro.org>
> ---
> ChangeLog v1->v2:
> - Fix spelling, terminology.
> 
> I make the patch to the OF core in this one, it makes much more sense since
> it's a oneliner
> 
> Lee: this is a (tested!) implementation of your suggestion for simple-mfd.
> If you can eventually ACK this from the MFD side, I think it should be
> funneled through the ARM SoC tree.
> 
> Grant/Rob: if either of you can ACK the change to the OF core likewise it can
> be taken through ARM SoC.
> 
> DT binings maintainers: there is some background discussion on this here:
> http://marc.info/?l=linux-arm-kernel&m=142486676603889&w=2
> http://marc.info/?l=devicetree&m=142166313621469&w=2
> ---
>  Documentation/devicetree/bindings/mfd/mfd.txt | 41 +++++++++++++++++++++++++++
>  drivers/of/platform.c                         |  1 +
>  2 files changed, 42 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/mfd/mfd.txt

Acked-by: Lee Jones <lee.jones@...aro.org>

> diff --git a/Documentation/devicetree/bindings/mfd/mfd.txt b/Documentation/devicetree/bindings/mfd/mfd.txt
> new file mode 100644
> index 000000000000..af9d6931a1a2
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/mfd/mfd.txt
> @@ -0,0 +1,41 @@
> +Multi-Function Devices (MFD)
> +
> +These devices comprise a nexus for heterogeneous hardware blocks containing
> +more than one non-unique yet varying hardware functionality.
> +
> +A typical MFD can be:
> +
> +- A mixed signal ASIC on an external bus, sometimes a PMIC (Power Management
> +  Integrated Circuit) that is manufactured in a lower technology node (rough
> +  silicon) that handles analog drivers for things like audio amplifiers, LED
> +  drivers, level shifters, PHY (physical interfaces to things like USB or
> +  ethernet), regulators etc.
> +
> +- A range of memory registers containing "miscellaneous system registers" also
> +  known as a system controller "syscon" or any other memory range containing a
> +  mix of unrelated hardware devices.
> +
> +Optional properties:
> +
> +- compatible : "simple-mfd" - this signifies that the operating system should
> +  consider all subnodes of the MFD device as separate devices akin to how
> +  "simple-bus" inidicates when to see subnodes as children for a simple
> +  memory-mapped bus. For more complex devices, when the nexus driver has to
> +  probe registers to figure out what child devices exist etc, this should not
> +  be used. In the latter case the child devices will be determined by the
> +  operating system.
> +
> +Example:
> +
> +foo@...0 {
> +	compatible = "syscon", "simple-mfd";
> +	reg = <0x01000 0x1000>;
> +
> +	led@...0 {
> +		compatible = "register-bit-led";
> +		offset = <0x08>;
> +		mask = <0x01>;
> +		label = "myled";
> +		default-state = "on";
> +	};
> +};
> diff --git a/drivers/of/platform.c b/drivers/of/platform.c
> index b189733a1539..969ba4e1460c 100644
> --- a/drivers/of/platform.c
> +++ b/drivers/of/platform.c
> @@ -26,6 +26,7 @@
>  
>  const struct of_device_id of_default_bus_match_table[] = {
>  	{ .compatible = "simple-bus", },
> +	{ .compatible = "simple-mfd", },
>  #ifdef CONFIG_ARM_AMBA
>  	{ .compatible = "arm,amba-bus", },
>  #endif /* CONFIG_ARM_AMBA */

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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