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

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 <redacted>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Devicetree <redacted>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Grant Likely <redacted>
Cc: Pawel Moll <redacted>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ian Campbell <redacted>
Cc: Kumar Gala <redacted>
Signed-off-by: Linus Walleij <redacted>
---
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.
+
+Example:
+
+foo at 1000 {
+		compatible = "syscon", "simple-mfd";
+		reg = <0x010000 0x1000>;
+
+		led at 08.0 {
+			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 */