Messages in this thread | | | Date | Tue, 1 Aug 2023 10:06:14 +0100 | Subject | Re: [PATCH v6 1/3] ABI: sysfs-nvmem-cells: Expose cells through sysfs | From | Srinivas Kandagatla <> |
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On 31/07/2023 16:51, Miquel Raynal wrote: > Hi John, > > Srinivas, a question for you below. > > lists@johnthomson.fastmail.com.au 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@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..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@bootlin.com> >>> +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@makrotopia.org/ > > 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@www.fastmail.com/ >> >>> + 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
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