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Subject: Re: [PATCH v2 3/3] dt-bindings: mtd: Document use of nvmem-partitions
 compatible
To:     Ansuel Smith <ansuelsmth@gmail.com>,
        Rob Herring <robh+dt@kernel.org>,
        Richard Weinberger <richard@nod.at>
Cc:     devicetree@vger.kernel.org, Vignesh Raghavendra <vigneshr@ti.com>,
        Boris Brezillon <bbrezillon@kernel.org>,
        linux-kernel@vger.kernel.org, linux-mtd@lists.infradead.org,
        Miquel Raynal <miquel.raynal@bootlin.com>
References: <20210216212638.28382-1-ansuelsmth@gmail.com>
 <20210216212638.28382-4-ansuelsmth@gmail.com>
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Date:   Wed, 3 Mar 2021 11:01:55 +0100
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[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@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@10 {
		reg = <0x10 0x4>;
	};

	firmware-date@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@0 {
	compatible = "vendor,dynamic-firmware-partitions";
	label = "firmware";
	reg = <0x0 0x100000>;
};

(...)

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

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


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