RE: [RFC 1/2] dt-bindings: imx-ocotp: Add fusable-node property

[Peng Fan]

Hi Rob, Srinivas

> Subject: [RFC 1/2] dt-bindings: imx-ocotp: Add fusable-node property

Do you have any comments about this patch?

Thanks,
Peng.

> 
> Introduce fusable-node property for i.MX OCOTP driver.
> The property will only be used by Firmware(eg. U-Boot) to runtime disable the
> nodes.
> 
> Take i.MX6ULL for example, there are several parts that only have limited
> modules enabled controlled by OCOTP fuse. It is not flexible to provide several
> dts for the serval parts, instead we could provide one device tree and let
> Firmware to runtime disable the device tree nodes for those modules that are
> disable(fused).
> 
> Signed-off-by: Peng Fan <peng.fan@xxxxxxx>
> ---
> 
> Currently NXP vendor use U-Boot to set status to disabled for devices that
> could not function,
> https://source.codeaurora.org/external/imx/uboot-imx/tree/arch/arm/mach
> -imx/mx6/module_fuse.c?h=imx_v2018.03_4.14.98_2.0.0_ga#n149
> But this approach is will not work if kernel dts node path changed.
> 
> There are two approaches to resolve:
> 
> 1. This patch is to add a fusable-node property, and Firmware will parse
>    the property and read fuse to decide whether to disable or keeep enable
>    the nodes.
> 
> 2. There is another approach is that add nvmem-cells for all nodes that
>    could be disabled(fused). Then in each linux driver to use nvmem
>    api to detect fused or not, or in linux driver common code to check
>    device functionable or not with nvmem API.
> 
> 
> To make it easy to work, we choose [1] here. Please advise whether it is
> acceptable, because the property is not used by linux driver in approach [1].
> Or you prefer [2] or please advise if any better solution.
> 
> Thanks.
> 
>  Documentation/devicetree/bindings/nvmem/imx-ocotp.txt | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/nvmem/imx-ocotp.txt
> b/Documentation/devicetree/bindings/nvmem/imx-ocotp.txt
> index 7a999a135e56..e9a998588dbd 100644
> --- a/Documentation/devicetree/bindings/nvmem/imx-ocotp.txt
> +++ b/Documentation/devicetree/bindings/nvmem/imx-ocotp.txt
> @@ -21,6 +21,8 @@ Required properties:
> 
>  Optional properties:
>  - read-only: disable write access
> +- fusable-node: array of phandles with reg base and bit offset, this
> +		property is used by Firmware to runtime disable nodes.
> 
>  Optional Child nodes:
> 
> @@ -42,4 +44,7 @@ Example:
>  		tempmon_temp_grade: temp-grade@20 {
>  			reg = <0x20 4>;
>  		};
> +
> +		fusable-node = <&usdhc1 0x10 4
> +				&usdhc2 0x10 5>;
>  	};
> --
> 2.16.4