On Mon, 22 May 2017, Masahiro Yamada wrote:
> 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?
You can use them interchangeably and they will 'work', but the
implication will be wrong. Hence why both exist.
> If so, I thought the example some lines below is questionable.
>
> ---------------------8<---------------------------
> 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";
> };
> };
> ---------------------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.
Correct. It would be inappropriate to use "simple-bus" for this use
case. That is most likely why "simple-mfd" is used instead.
> 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@10000000/led@08.0 missing or empty reg/ranges
> property
> arch/arm/boot/dts/arm-realview-pb1176.dtb: Warning (simple_bus_reg):
> Node /soc/syscon@10000000/led@08.1 missing or empty reg/ranges
> property
> arch/arm/boot/dts/arm-realview-pb1176.dtb: Warning (simple_bus_reg):
> Node /soc/syscon@10000000/led@08.2 missing or empty reg/ranges
> property
> arch/arm/boot/dts/arm-realview-pb1176.dtb: Warning (simple_bus_reg):
> Node /soc/syscon@10000000/led@08.3 missing or empty reg/ranges
> property
> arch/arm/boot/dts/arm-realview-pb1176.dtb: Warning (simple_bus_reg):
> Node /soc/syscon@10000000/led@08.4 missing or empty reg/ranges
> property
> arch/arm/boot/dts/arm-realview-pb1176.dtb: Warning (simple_bus_reg):
> Node /soc/syscon@10000000/led@08.5 missing or empty reg/ranges
> property
> arch/arm/boot/dts/arm-realview-pb1176.dtb: Warning (simple_bus_reg):
> Node /soc/syscon@10000000/led@08.6 missing or empty reg/ranges
> property
> arch/arm/boot/dts/arm-realview-pb1176.dtb: Warning (simple_bus_reg):
> Node /soc/syscon@10000000/led@08.7 missing or empty reg/ranges
> property
> arch/arm/boot/dts/arm-realview-pb1176.dtb: Warning (simple_bus_reg):
> Node /soc/syscon@10000000/osc0@0c missing or empty reg/ranges property
> arch/arm/boot/dts/arm-realview-pb1176.dtb: Warning (simple_bus_reg):
> Node /soc/syscon@10000000/osc1@10 missing or empty reg/ranges property
> arch/arm/boot/dts/arm-realview-pb1176.dtb: Warning (simple_bus_reg):
> Node /soc/syscon@10000000/osc2@14 missing or empty reg/ranges property
> arch/arm/boot/dts/arm-realview-pb1176.dtb: Warning (simple_bus_reg):
> Node /soc/syscon@10000000/osc3@18 missing or empty reg/ranges property
> arch/arm/boot/dts/arm-realview-pb1176.dtb: Warning (simple_bus_reg):
> Node /soc/syscon@10000000/osc4@1c missing or empty reg/ranges property
Exactly. Don't do that. :)
--
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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