[PATCH v2 3/3] dt-bindings: mtd: Document use of nvmem-partitions compatible

[Rafał Miłecki]

[Rob: please advise]

On 16.02.2021 22:26, Ansuel Smith wrote:
> Document nvmem-partitions compatible used to treat mtd partitions as a
> nvmem provider.

Until now we were using "compatible" string in partition node only for
parsers (looking for subpartitions). We need to think if this change can
break anything from DT / Linux perspective.

Compatible strings should be unique, so there is no risk of conflict
between NVMEM and parsers.

Now: can we ever need mtd partition to:
1. Contain subpartitions
2. Provide NVMEM
at the same time?

Let's say:

partition at 0 {
	compatible = "vendor,dynamic-firmware-partitions", "nvmem-partitions";
	label = "firmware";
	reg = <0x0 0x100000>;
	#address-cells = <1>;
	#size-cells = <1>;
	ranges = <0 0x0 0x100000>;

	firmware-version at 10 {
		reg = <0x10 0x4>;
	};

	firmware-date at 10 {
		reg = <0x20 0x4>;
	};
};

Is that allowed to respect both "compatible" strings and have:
1. Linux parser parse "firmware" for subpartitions
2. Linux MTD register "firmware" as NVMEM device
?

If not, what other options do we have? Is that allowed to have a
dangling MTD NVMEM node with phandle to MTD partition?

firmware: partition at 0 {
	compatible = "vendor,dynamic-firmware-partitions";
	label = "firmware";
	reg = <0x0 0x100000>;
};

(...)

firmware-version at 10 {
	compatible = "mtd-nvmem";
	reg = <0x10 0x4>;
	mtd = <&firmware>;
};

firmware-date at 10 {
	compatible = "mtd-nvmem";
	reg = <0x20 0x4>;
	mtd = <&firmware>;
};


Rob: I'd really appreciate your input & help here.