[DT Question] "simple-mfd" DT binding

[Masahiro Yamada]

Hi DT experts,

I have a question about "simple-mfd".


Documentation/devicetree/bindings/mfd/mfd.txt says as allows:

----------------------8<---------------------
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" indicates when to see subnodes as children for a simple
  memory-mapped bus.   <snip>
----------------------8<---------------------


I'd like to be sure about the statement above.

Does this mean, "simple-bus" and "simple-mfd" are technically interchangeable?



If so, I thought the example some lines below is questionable.

---------------------8<---------------------------
Example:

foo at 1000 {
        compatible = "syscon", "simple-mfd";
        reg = <0x01000 0x1000>;

        led at 08.0 {
                compatible = "register-bit-led";
                offset = <0x08>;
                mask = <0x01>;
                label = "myled";
                default-state = "on";
        };
};
---------------------8<---------------------------


Because "simple-bus" indicates that child nodes are
simply memory mapped, but the node "register-bit-led"
can not be memory-mapped.
So, "simple-mfd" can not be replaced "simple-bus" here.



arch/arm/boot/dts/arm-realview-pb1176.dts is a real example.

If I replace "simple-mfd" with "simple-bus",
DTC warns "empty reg/ranges property".



$ sed -i  -e 's/simple-mfd/simple-bus/'
arch/arm/boot/dts/arm-realview-pb1176.dts
$ make -s ARCH=arm defconfig
$ make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- W=1  arm-realview-pb1176.dtb
   ...
arch/arm/boot/dts/arm-realview-pb1176.dtb: Warning (simple_bus_reg):
Node /soc/syscon at 10000000/led at 08.0 missing or empty reg/ranges
property
arch/arm/boot/dts/arm-realview-pb1176.dtb: Warning (simple_bus_reg):
Node /soc/syscon at 10000000/led at 08.1 missing or empty reg/ranges
property
arch/arm/boot/dts/arm-realview-pb1176.dtb: Warning (simple_bus_reg):
Node /soc/syscon at 10000000/led at 08.2 missing or empty reg/ranges
property
arch/arm/boot/dts/arm-realview-pb1176.dtb: Warning (simple_bus_reg):
Node /soc/syscon at 10000000/led at 08.3 missing or empty reg/ranges
property
arch/arm/boot/dts/arm-realview-pb1176.dtb: Warning (simple_bus_reg):
Node /soc/syscon at 10000000/led at 08.4 missing or empty reg/ranges
property
arch/arm/boot/dts/arm-realview-pb1176.dtb: Warning (simple_bus_reg):
Node /soc/syscon at 10000000/led at 08.5 missing or empty reg/ranges
property
arch/arm/boot/dts/arm-realview-pb1176.dtb: Warning (simple_bus_reg):
Node /soc/syscon at 10000000/led at 08.6 missing or empty reg/ranges
property
arch/arm/boot/dts/arm-realview-pb1176.dtb: Warning (simple_bus_reg):
Node /soc/syscon at 10000000/led at 08.7 missing or empty reg/ranges
property
arch/arm/boot/dts/arm-realview-pb1176.dtb: Warning (simple_bus_reg):
Node /soc/syscon at 10000000/osc0 at 0c missing or empty reg/ranges property
arch/arm/boot/dts/arm-realview-pb1176.dtb: Warning (simple_bus_reg):
Node /soc/syscon at 10000000/osc1 at 10 missing or empty reg/ranges property
arch/arm/boot/dts/arm-realview-pb1176.dtb: Warning (simple_bus_reg):
Node /soc/syscon at 10000000/osc2 at 14 missing or empty reg/ranges property
arch/arm/boot/dts/arm-realview-pb1176.dtb: Warning (simple_bus_reg):
Node /soc/syscon at 10000000/osc3 at 18 missing or empty reg/ranges property
arch/arm/boot/dts/arm-realview-pb1176.dtb: Warning (simple_bus_reg):
Node /soc/syscon at 10000000/osc4 at 1c missing or empty reg/ranges property






-- 
Best Regards
Masahiro Yamada