[RESEND,v5,1/3] 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 | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-nvmem-cells
  

Hi,

On 7/13/23 00:55, 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 | 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..641a7d7dad76
> --- /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@bootlin.com>
> +Description:
> +		The cells/ folder contains one file per cell exposed by

(My shell doesn't show "folders". ;)

> +		the nvmem device. The name of the file is the cell name.
> +		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

add ending '.':    enabled.

> +
> +		ex::

		Example::
or
		E.g.::

> +
> +		  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
  

Hi Randy,

rdunlap@infradead.org wrote on Thu, 13 Jul 2023 08:56:48 -0700:

> Hi,
> 
> On 7/13/23 00:55, 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 | 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..641a7d7dad76
> > --- /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@bootlin.com>
> > +Description:
> > +		The cells/ folder contains one file per cell exposed by  
> 
> (My shell doesn't show "folders". ;)

What do you mean? Is it your shell that needs fixing? Or is it
something that I need to fix?

> > +		the nvmem device. The name of the file is the cell name.
> > +		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  
> 
> add ending '.':    enabled.
> 
> > +
> > +		ex::  
> 
> 		Example::

Yup, I'll fix it in v6.

> or
> 		E.g.::
> 
> > +
> > +		  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  
> 


Thanks,
Miquèl