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SubjectRe: [PATCH 2/2] nvmem: expose NVMEM cells in sysfs
Hi Rafał,

Thank you for working on this.
I hacked together the same functionality based on kernel 5.10 some months ago,
while I was testing an MTD parser based TLV NVMEM cells parser,
and have some general comments.

On Mon, 20 Dec 2021, at 06:47, Rafał Miłecki wrote:
> From: Rafał Miłecki <rafal@milecki.pl>
>
> This allows reading NVMEM cells using /sys/bus/nvmem/devices/*/cells/*
> which may be helpful for userspace & debugging purposes.
>
> Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
> ---
> Documentation/driver-api/nvmem.rst | 11 ++++++
> drivers/nvmem/core.c | 60 ++++++++++++++++++++++++++++++
> 2 files changed, 71 insertions(+)
>
> diff --git a/Documentation/driver-api/nvmem.rst
> b/Documentation/driver-api/nvmem.rst
> index 287e86819640..20f7d68143be 100644
> --- a/Documentation/driver-api/nvmem.rst
> +++ b/Documentation/driver-api/nvmem.rst
> @@ -185,6 +185,17 @@ ex::
> *
> 0001000
>
> +Single cells can be read using files located at::
> +
> + /sys/bus/nvmem/devices/*/cells/*
> +
> +ex::
> +
> + hexdump -C /sys/bus/nvmem/devices/mtd0/cells/mac

I found that NVMEM cell names did not need to be unique, but sysfs entry names do.
I am not sure if there are characters that NVMEM cell names allow,
but sysfs entry names forbid.
I used an ID allocator, in a similar style to what is done for MTD sysfs devices in mtdcore.c.

Could the cell (data) binary attribute be in a subfolder for each cell?
Example:
/sys/bus/nvmem/devices/mtd0/cells/cell0/cell
or
/sys/bus/nvmem/devices/mtd0/cells/cell0/cell_data

This way, we can easily expose additional properties of the cell.
I exposed the name, offset, bytes, bit_offset, and an of_node link (where available) this way.
I only needed these for testing, but the cell length (bytes) provided a cheap means for initial validation.

I did not look into cell post-processing, but it should be considered:
https://lore.kernel.org/all/20211006144729.15268-1-srinivas.kandagatla@linaro.org/
and RFC https://lore.kernel.org/all/CAL_JsqL55mZJ6jUyQACer2pKMNDV08-FgwBREsJVgitnuF18Cg@mail.gmail.com/
Will the cell data exposed here be prior to post-processing?


Thank you

Cheers,
--
John Thomson

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