Re: [PATCH v6 1/3] ABI: sysfs-nvmem-cells: Expose cells through sysfs

[Srinivas Kandagatla]

On 31/07/2023 16:51, Miquel Raynal wrote:
> Hi John,
>
> Srinivas, a question for you below.
>
> lists@xxxxxxxxxxxxxxxxxxxxxxxxxxx wrote on Sun, 23 Jul 2023 19:39:50
> +0000:
>
> > Hi Miquel,
> >
> > On Mon, 17 Jul 2023, at 07:51, 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@xxxxxxxxxxx>
> > > Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > > ---
> > >   Documentation/ABI/testing/sysfs-nvmem-cells | 19 +++++++++++++++++++
> > >   1 file changed, 19 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..b2d15a8d36e5
> > > --- /dev/null
> > > +++ b/Documentation/ABI/testing/sysfs-nvmem-cells
> > > @@ -0,0 +1,19 @@
> > > +What:		/sys/bus/nvmem/devices/.../cells/<cell-name>
> > > +Date:		May 2023
> > > +KernelVersion:	6.5
> > > +Contact:	Miquel Raynal <miquel.raynal@xxxxxxxxxxx>
> > > +Description:
> > > +		The "cells" folder contains one file per cell exposed by
> > > +		the nvmem device. The name of the file is the cell name.
> >
> > Could we consider using a file within a folder (name defined by cell propertys) to access the cell bytes?
> > Example (pick the best path and filename):
> > /sys/bus/nvmem/devices/.../cells/<cell-name>/bytes
> >
> > That way, it is much easier to expand this at a later stage,
> > like adding an of_node link at
> > /sys/bus/nvmem/devices/.../cells/<cell-name>/of_node
> > or exposing other nvmem cell properties.
>
> I have no strong opinion. Srinivas what do you prefer? I'm fine either
> ways. I like the simplicity of the current approach more, but it's true
> that it is more easy to make it grow if we follow John idea.

Sounds sensible to me.


> > This is particularly relevant given the cell-name alone does not always
> > uniquely represent a cell on an nvmem device.
> > https://lore.kernel.org/lkml/ZLaZ7fzUSsa0Igx1@xxxxxxxxxxxxxx/
>
> It seems like this is gonna be fixed by suffixing @<offset> to the
> name, as anyway whatever solution we choose, it is gonna be needed.

we have to be careful here not to break the nvmem_cell_get() users.


--srini


> > https://lore.kernel.org/lkml/e7173ab2-d3b2-4f75-beb8-32593b868774@xxxxxxxxxxxxxxxx/
> >
> > > +		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
> > > +		  00000000  54 4e 34 38 4d 2d 50 2d  44 4e         |TN48M-P-DN|
> > > +		  0000000a
> > > --
> > > 2.34.1
> >
> > Cheers,
>
>
> Thanks,
> Miquèl