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

Rob Herring robherring2 at gmail.com
Tue Mar 3 09:47:44 PST 2015

On Tue, Mar 3, 2015 at 3:32 AM, Linus Walleij <linus.walleij at linaro.org> 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 at linaro.org>
> Cc: Arnd Bergmann <arnd at arndb.de>
> Cc: Devicetree <devicetree at vger.kernel.org>
> Cc: Rob Herring <robh+dt at kernel.org>
> Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org>
> Cc: Grant Likely <grant.likely at linaro.org>
> Cc: Pawel Moll <pawel.moll at arm.com>
> Cc: Mark Rutland <mark.rutland at arm.com>
> Cc: Ian Campbell <ijc+devicetree at hellion.org.uk>
> Cc: Kumar Gala <galak at codeaurora.org>
> Signed-off-by: Linus Walleij <linus.walleij at linaro.org>
> ---
> 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 | 40 +++++++++++++++++++++++++++
>  drivers/of/platform.c                         |  1 +
>  2 files changed, 41 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/mfd/mfd.txt
> diff --git a/Documentation/devicetree/bindings/mfd/mfd.txt b/Documentation/devicetree/bindings/mfd/mfd.txt
> new file mode 100644
> index 000000000000..cc057438abe8
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/mfd/mfd.txt
> @@ -0,0 +1,40 @@
> +Multi-Function Devices (MFD)
> +
> +These devices comprise a nexus for heterogeneous hardware blocks spawning
> +multiple child devices.
> +
> +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 registers.
> +
> +Optional properties:
> +
> +- compatible : "simple-mfd" - this signifies that the operating system should
> +  spawn child devices for all the subnodes of the MFD device akin to how
> +  "simple-bus" inidicates when to spawn children for a simple memory-mapped
> +  bus. For more complex devices, when the nexus driver has to probe registers
> +  to figure out what children exist etc, this should not be used. In the latter
> +  case the child devices will be instantiated by the operating system.

If you point of_platform_populate to the parent node, it should
instantiate all children regardless of "simple-bus" or any other
match. The match is to probe the grandchildren. I could be mistaken,
but that's how it works at the root level. You don't have a driver
probe for the parent, so you want the top level of_platform_populate
call to instantiate these devices?

Why does simple-bus not work for you? After all, it is not


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