linux-kernel - Re: [PATCH v7 6/7] ABI: sysfs-nvmem-cells: Expose cells through sysfs

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Message-ID: <20230807092047.1525e6a5@xps-13>
Date:   Mon, 7 Aug 2023 09:20:47 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Daniel Golle <daniel@...rotopia.org>
Cc:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Robert Marko <robert.marko@...tura.hr>,
        Luka Perkov <luka.perkov@...tura.hr>,
        Michael Walle <michael@...le.cc>, linux-kernel@...r.kernel.org,
        Randy Dunlap <rdunlap@...radead.org>,
        Chen-Yu Tsai <wenst@...omium.org>,
        Rafał Miłecki <rafal@...ecki.pl>
Subject: Re: [PATCH v7 6/7] ABI: sysfs-nvmem-cells: Expose cells through
 sysfs

Hi Daniel,

daniel@...rotopia.org wrote on Sat, 5 Aug 2023 15:50:41 +0100:

> On Tue, Aug 01, 2023 at 08:21:31PM +0200, Miquel Raynal wrote:
> > The binary content of nvmem devices is available to the user so in the
> > easiest cases, finding the content of a cell is rather easy as it is
> > just a matter of looking at a known and fixed offset. However, nvmem
> > layouts have been recently introduced to cope with more advanced
> > situations, where the offset and size of the cells is not known in
> > advance or is dynamic. When using layouts, more advanced parsers are
> > used by the kernel in order to give direct access to the content of each
> > cell regardless of their position/size in the underlying device, but
> > these information were not accessible to the user.
> > 
> > By exposing the nvmem cells to the user through a dedicated cell/ folder
> > containing one file per cell, we provide a straightforward access to
> > useful user information without the need for re-writing a userland
> > parser. Content of nvmem cells is usually: product names, manufacturing
> > date, MAC addresses, etc,
> > 
> > Signed-off-by: Miquel Raynal <miquel.raynal@...tlin.com>
> > Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > ---
> >  Documentation/ABI/testing/sysfs-nvmem-cells | 21 +++++++++++++++++++++
> >  1 file changed, 21 insertions(+)
> >  create mode 100644 Documentation/ABI/testing/sysfs-nvmem-cells
> > 
> > diff --git a/Documentation/ABI/testing/sysfs-nvmem-cells b/Documentation/ABI/testing/sysfs-nvmem-cells
> > new file mode 100644
> > index 000000000000..a1d140dcbd5d
> > --- /dev/null
> > +++ b/Documentation/ABI/testing/sysfs-nvmem-cells
> > @@ -0,0 +1,21 @@
> > +What:		/sys/bus/nvmem/devices/.../cells/<cell-name>
> > +Date:		May 2023
> > +KernelVersion:	6.5
> > +Contact:	Miquel Raynal <miquel.raynal@...tlin.com>
> > +Description:
> > +		The "cells" folder contains one file per cell exposed by the
> > +		NVMEM device. The name of the file is: <name>@<where>, with
> > +		<name> being the cell name and <where> its location in the NVMEM
> > +		device, in hexadecimal (without the '0x' prefix, to mimic device
> > +		tree node names). The length of the file is the size of the cell
> > +		(when known). The content of the file is the binary content of
> > +		the cell (may sometimes be ASCII, likely without trailing
> > +		character).
> > +		Note: This file is only present if CONFIG_NVMEM_SYSFS
> > +		is enabled.
> > +
> > +		Example::
> > +
> > +		  hexdump -C /sys/bus/nvmem/devices/1-00563/cells/product-name  
> 
> Location is missing here, should be something like
>   hexdump -C /sys/bus/nvmem/devices/1-00563/cells/product-name@f00

Yes. I forgot to update the cover letter as well. I will do it in next
version.

Thanks,
Miquèl