linux-kernel - Re: [PATCH] nvmem: imx-ocotp: read uniq CPU ID and export as system serial number

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Message-ID: <20171004154428.GK23092@leverpostej>
Date:   Wed, 4 Oct 2017 16:44:29 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Marcus Folkesson <marcus.folkesson@...il.com>
Cc:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nvmem: imx-ocotp: read uniq CPU ID and export as system
 serial number

On Wed, Oct 04, 2017 at 05:16:16PM +0200, Marcus Folkesson wrote:
> The uniq ID is usually exported as ATAG_SERIAL but in case of
> devicetrees, this information is not passed.
> 
> The uniq ID is stored in OCOTP memory (bank 0, Word 1,2) on imx CPUs.
> Read the ID and set as system serial number.
> 
> This function is activated by setting `read-system-serial`
> dt property for the imx-ocotp node.
> 
> Signed-off-by: Marcus Folkesson <marcus.folkesson@...il.com>
> ---
> 
> Comment:
> I'm not sure if this functionality really should be in a device driver.
> Maybe it should be in arch/arm/mach-imx/. However, it's not
> completely wrong so I give it a shot.
> 
>  .../devicetree/bindings/nvmem/imx-ocotp.txt        |  1 +
>  drivers/nvmem/imx-ocotp.c                          | 38 ++++++++++++++++++++++
>  2 files changed, 39 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/nvmem/imx-ocotp.txt b/Documentation/devicetree/bindings/nvmem/imx-ocotp.txt
> index 70d791b03ea1..bf0cc9e5e50f 100644
> --- a/Documentation/devicetree/bindings/nvmem/imx-ocotp.txt
> +++ b/Documentation/devicetree/bindings/nvmem/imx-ocotp.txt
> @@ -16,6 +16,7 @@ Required properties:
>  
>  Optional properties:
>  - read-only: disable write access
> +- read-system-serial: read uniq ID and export as system serial number. Available in /proc/cpuinfo

As described, this is a pure SW option (

/proc/cpuinfo is a not a HW detail, and whether or not to export this
information there is a policy. So as described, this shouldn't be in the
DT.

Are you just trying to describe whether hte information is available in
the OCOTP memory?

e.g. maybe this should be something like:

- has-unique-id: OCOTP bank0, Words 1 & 2 contain a unique ID
  identifying the system.

Thanks,
Mark.