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authorLinus Walleij <linus.walleij@linaro.org>2015-03-03 09:52:20 +0100
committerAlex Shi <alex.shi@linaro.org>2015-11-07 21:52:49 +0800
commitbcc8381710a050b6dc84170602dc4fcf2140d510 (patch)
tree557a90d98990c2506424449e38a117a4a7e865f6 /Documentation
parentc10307cbf8be7aa5410ad04f780bdeb43ba8f294 (diff)
downloadlinux-linaro-stable-bcc8381710a050b6dc84170602dc4fcf2140d510.tar.gz
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 <lee.jones@linaro.org> Acked-by: Lee Jones <lee.jones@linaro.org> Acked-by: Antoine Tenart <antoine.tenart@free-electrons.com> Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Devicetree <devicetree@vger.kernel.org> Cc: Rob Herring <robh+dt@kernel.org> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Grant Likely <grant.likely@linaro.org> Cc: Pawel Moll <pawel.moll@arm.com> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Ian Campbell <ijc+devicetree@hellion.org.uk> Cc: Kumar Gala <galak@codeaurora.org> Signed-off-by: Linus Walleij <linus.walleij@linaro.org> (cherry picked from commit 22869a9eca4ea5b534538d160b68c7aef44e378a) Signed-off-by: Alex Shi <alex.shi@linaro.org>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/devicetree/bindings/mfd/mfd.txt41
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diff --git a/Documentation/devicetree/bindings/mfd/mfd.txt b/Documentation/devicetree/bindings/mfd/mfd.txt
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+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@1000 {
+ compatible = "syscon", "simple-mfd";
+ reg = <0x01000 0x1000>;
+
+ led@08.0 {
+ compatible = "register-bit-led";
+ offset = <0x08>;
+ mask = <0x01>;
+ label = "myled";
+ default-state = "on";
+ };
+};