Re: [RFC/PATCH 1/2] doc: bindings: Add bindings documentation for mtd otp nvmem

Boris Brezillon
2016-05-26T08:04:39Z

Hi Moritz,

On Wed, 25 May 2016 14:26:46 -0700
Moritz Fischer <moritz.fischer@ettus.com> wrote:

> This commit adds documentation describing the bindings for
> exposing mtd flash otp regions as nvmem providers via devicetree.
>
> Signed-off-by: Moritz Fischer <moritz.fischer@ettus.com>
> ---
> .../devicetree/bindings/mtd/otp-nvmem.txt | 62 ++++++++++++++++++++++
> 1 file changed, 62 insertions(+)
> create mode 100644 Documentation/devicetree/bindings/mtd/otp-nvmem.txt
>
> diff --git a/Documentation/devicetree/bindings/mtd/otp-nvmem.txt b/Documentation/devicetree/bindings/mtd/otp-nvmem.txt
> new file mode 100644
> index 0000000..a83a7da
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/mtd/otp-nvmem.txt
> @@ -0,0 +1,62 @@
> +Representing OTP regions in devicetree
> +
> +OTP regions can be represented by sub-nodes of an mtd device.
> +
> +The partition table should be a subnode of the mtd node and should be names
> +'otp-partitions'. This node should have the following property:
> +
> +- compatible: (required) must be 'fixed-partitions'
> +
> +OTP regions are then defined in subnodes of the partitions node.
> +
> +Required properties for OTP regions:
> +- reg: The region's offset and size within the mtd device
> +
> +Optional properties:
> +- label: The label / name for this region. If ommited, the label is taken
> + from the node name (excluding the unit address).
> +
> +Example:
> +
> +flash@0 {
> + partitions {
> + compatible = "fixed-partitions";
> + #address-cells = <1>;
> + #size-cells = <1>;
> +
> + partition@0 {
> + label = "uboot-spl";
> + reg = <0x0 0xe0000>;
> + };
> + partition@1 {
> + label = "uboot-env";
> + reg = <0xe0000 0x20000>;
> + };
> + partition@2 {
> + label = "uboot";
> + reg = <0x100000 0x100000>;
> + };
> + };
> +
> + otp-partitions {
> + compatible = "fixed-partitions";
> + #address-cells = <1>;
> + #size-cells = <1>;
> +
> + region@0 {
> + label = "factory-data";
> + reg = <0x0 0x40>;
> +
> + #address-cells = <0x1>;
> + #size-cells = <0x1>;
> +
> + product: nvmem@0 {
> + reg = <0x0 0x2>;
> + };
> +
> + revision: nvmem@3 {
> + reg = <0x3 0x2>;
> + };
> + };
> + };
> +}

I think the MTD partition -> nvmem connection could benefit to non-OTP
partitions too.

So, how about defining the nvmem regions under the partition nodes,
like that:

flash@0 {
partitions {
compatible = "fixed-partitions";
#address-cells = <1>;
#size-cells = <1>;

partition@0 {
label = "uboot-spl";
reg = <0x0 0xe0000>;
};

/* ... */

partition@X{
label = "factory-data-part";
reg = <0x200000 0x100000>;
#address-cells = <1>;
#size-cells = <1>;

product: nvmem@0 {
reg = <0x0 0x2>;
};

revision: nvmem@3 {
reg = <0x3 0x2>;
};
};
};

otp-partitions {
compatible = "fixed-partitions";
#address-cells = <1>;
#size-cells = <1>;

partition@X{
label = "factory-data-part";
reg = <0x0 0x40>;
#address-cells = <1>;
#size-cells = <1>;

product: nvmem@0 {
reg = <0x0 0x2>;
};

revision: nvmem@3 {
reg = <0x3 0x2>;
};
};
};
};

I know this requires changing the implementation to select the
appropriate nvmem wrapper to use depending on whether we're interfacing
with an OTP area or a regular one, but that should be doable.

Regards,

Boris

--
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering