linux-kernel - Re: [PATCH V2] dt-bindings: nvmem: u-boot,env: add Broadcom's variant binding

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Message-ID: <166578177913.2909910.7600034251484225468.robh@kernel.org>
Date:   Fri, 14 Oct 2022 16:09:40 -0500
From:   Rob Herring <robh@...nel.org>
To:     Rafał Miłecki <zajec5@...il.com>
Cc:     Rafał Miłecki <rafal@...ecki.pl>,
        William Zhang <william.zhang@...adcom.com>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Joel Peshkin <joel.peshkin@...adcom.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        bcm-kernel-feedback-list@...adcom.com,
        linux-arm-kernel@...ts.infradead.org,
        Rob Herring <robh+dt@...nel.org>,
        Tom Rini <trini@...sulko.com>, u-boot@...ts.denx.de,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] dt-bindings: nvmem: u-boot,env: add Broadcom's
 variant binding

On Fri, 30 Sep 2022 18:36:31 +0200, Rafał Miłecki wrote:
> From: Rafał Miłecki <rafal@...ecki.pl>
> 
> Broadcom uses U-Boot for a lot of their bcmbca familiy chipsets. U-Boot
> stores its configuration in an environment data block.
> 
> Such blocks are usually stored on flash as a separated partition at
> hardcoded address. Broadcom however decided to:
> 1. Store env data block inside U-Boot partition
> 2. Avoid sticking to hardcoded offsets
> 3. Use custom header with "uEnv" magic and env data length
> 
> Example (length 0x4000):
> $ hexdump -n 32 -C -s 0x40000 /dev/mtdblock0
> 00040000  76 6e 45 75 00 40 00 00  34 89 7a 82 49 4d 41 47  |vnEu.@....z.IMAG|
> 00040010  45 3d 4e 41 4e 44 3a 31  4d 2c 31 30 32 34 4d 00  |E=NAND:1M,1024M.|
> (0x40000 offset is unit specific and can change)
> 
> Starting with the commit 118f3fbe517f4 ("dt-bindings: mtd: partitions:
> support label/name only partition") DT can describe partitions matching
> them by a name (without specifying actual address). With that feature
> and this binding change it's possible to:
> 1. Specify DT node for Broadcom's U-Boot env data subpartition
> 2. Add nodes for specific environment data variables
> 3. Reference them as NVMEM cells
> 
> This binding is unlikely to help Broadcom's U-Boot. U-Boot SPL needs to
> find environment data early (before it accesses DTB) and it does that by
> looking for an "uEnv" magic. Dirty way.
> 
> This binding can however be used by operating systems. It allows
> describing cleanly U-Boot, its env data and variables. It tells
> operating system about Broadcom-specific env data so it can parse it.
> 
> Signed-off-by: Rafał Miłecki <rafal@...ecki.pl>
> ---
> V2: Work on better commit body & add example
> ---
>  .../devicetree/bindings/nvmem/u-boot,env.yaml | 21 +++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 

Applied, thanks!