[v7,6/7] ABI: sysfs-nvmem-cells: Expose cells through sysfs

  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@bootlin.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 Documentation/ABI/testing/sysfs-nvmem-cells | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-nvmem-cells
  

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@bootlin.com>
> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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@bootlin.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

> +		  00000000  54 4e 34 38 4d 2d 50 2d  44 4e         |TN48M-P-DN|
> +		  0000000a
> -- 
> 2.34.1
>
  

Hi Daniel,

daniel@makrotopia.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@bootlin.com>
> > Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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@bootlin.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