[PATCH v12 0/7] NVMEM cells in sysfs

Miquel Raynal
2023-10-05T16:19:05Z

Hello,

As part of a previous effort, support for dynamic NVMEM layouts was
brought into mainline, helping a lot in getting information from NVMEM
devices at non-static locations. One common example of NVMEM cell is the
MAC address that must be used. Sometimes the cell content is mainly (or
only) useful to the kernel, and sometimes it is not. Users might also
want to know the content of cells such as: the manufacturing place and
date, the hardware version, the unique ID, etc. Two possibilities in
this case: either the users re-implement their own parser to go through
the whole device and search for the information they want, or the kernel
can expose the content of the cells if deemed relevant. This second
approach sounds way more relevant than the first one to avoid useless
code duplication, so here is a series bringing NVMEM cells content to
the user through sysfs.

Here is a real life example with a Marvell Armada 7040 TN48m switch:

$ nvmem=/sys/bus/nvmem/devices/1-00563/
$ for i in `ls -1 $nvmem/cells/*`; do basename $i; hexdump -C $i | head -n1; done
country-code@77
00000000 54 57 |TW|
crc32@88
00000000 bb cd 51 98 |..Q.|
device-version@49
00000000 02 |.|
diag-version@80
00000000 56 31 2e 30 2e 30 |V1.0.0|
label-revision@4c
00000000 44 31 |D1|
mac-address@2c
00000000 18 be 92 13 9a 00 |......|
manufacture-date@34
00000000 30 32 2f 32 34 2f 32 30 32 31 20 31 38 3a 35 39 |02/24/2021 18:59|
manufacturer@72
00000000 44 4e 49 |DNI|
num-macs@6e
00000000 00 40 |.@|
onie-version@61
00000000 32 30 32 30 2e 31 31 2d 56 30 31 |2020.11-V01|
platform-name@50
00000000 38 38 46 37 30 34 30 2f 38 38 46 36 38 32 30 |88F7040/88F6820|
product-name@d
00000000 54 4e 34 38 4d 2d 50 2d 44 4e |TN48M-P-DN|
serial-number@19
00000000 54 4e 34 38 31 50 32 54 57 32 30 34 32 30 33 32 |TN481P2TW2042032|
vendor@7b
00000000 44 4e 49 |DNI|

Current support does not include:
* The knowledge of the type of data (binary vs. ASCII), so by default
all cells are exposed in binary form.
* Write support.

Changes in v12:
* Fixed the issues reported by kernel test robot.
* Reworked even deeper the registration of layout devices and dropped
all the research and matching code that was previously needed as
suggested by Srinivas. This way, we no longer use the notifiers.

Changes in v11:
* The nvmem layouts are now regular devices and not platform devices
anymore. They are registered into the nvmem-layout bus (so there is a
new /sysfs/bus/nvmem-layouts entry that gets created. All the code for
this new bus is located under drivers/nvmem/layouts.c and is part of
the main core. The core device-driver logic applies without too much
additional code besides the registration of the bus and a bit of
glue. I see no need for more detailed structures for now but this can
be improved later as needed.

Changes in v10:
* All preparation patches have been picked-up by Srinivas.
* Rebased on top of v6.6-rc1.
* Fix an error path in the probe due to the recent additions.

Changes in v9:
* Hopefully fixed the creation of sysfs entries when describing the
cells using the legacy layout, as reported by Chen-Yu.
* Dropped the nvmem-specific device list and used the driver core list
instead as advised by Greg.

Changes in v8:
* Fix a compilation warning whith !CONFIG_NVMEM_SYSFS.
* Add a patch to return NULL when no layout is found (reported by Dan
Carpenter).
* Fixed the documentation as well as the cover letter regarding the
addition of addresses in the cell names.

Changes in v7:
* Rework the layouts registration mechanism to use the platform devices
logic.
* Fix the two issues reported by Daniel Golle and Chen-Yu Tsai, one of
them consist in suffixing '@<offset>' to the cell name to create the
sysfs files in order to be sure they are all unique.
* Update the doc.

Changes in v6:
* ABI documentation style fixes reported by Randy Dunlap:
s|cells/ folder|"cells" folder|
Missing period at the end of the final note.
s|Ex::|Example::|
* Remove spurious patch from the previous resubmission.

Resending v5:
* I forgot the mailing list in my former submission, both are absolutely
identical otherwise.

Changes in v5:
* Rebased on last -rc1, fixing a conflict and skipping the first two
patches already taken by Greg.
* Collected tags from Greg.
* Split the nvmem patch into two, one which just moves the cells
creation and the other which adds the cells.

Changes in v4:
* Use a core helper to count the number of cells in a list.
* Provide sysfs attributes a private member which is the entry itself to
avoid the need for looking up the nvmem device and then looping over
all the cells to find the right one.

Changes in v3:
* Patch 1 is new: fix a style issue which bothered me when reading the
core.
* Patch 2 is new: Don't error out when an attribute group does not
contain any attributes, it's easier for developers to handle "empty"
directories this way. It avoids strange/bad solutions to be
implemented and does not cost much.
* Drop the is_visible hook as it is no longer needed.
* Stop allocating an empty attribute array to comply with the sysfs core
checks (this check has been altered in the first commits).
* Fix a missing tab in the ABI doc.

Changes in v2:
* Do not mention the cells might become writable in the future in the
ABI documentation.
* Fix a wrong return value reported by Dan and kernel test robot.
* Implement .is_bin_visible().
* Avoid overwriting the list of attribute groups, but keep the cells
attribute group writable as we need to populate it at run time.
* Improve the commit messages.
* Give a real life example in the cover letter.

Miquel Raynal (7):
of: device: Export of_device_make_bus_id()
nvmem: Clarify the situation when there is no DT node available
nvmem: Move of_nvmem_layout_get_container() in another header
nvmem: Create a header for internal sharing
nvmem: core: Rework layouts to become regular devices
ABI: sysfs-nvmem-cells: Expose cells through sysfs
nvmem: core: Expose cells through sysfs

Documentation/ABI/testing/sysfs-nvmem-cells | 21 ++
drivers/nvmem/Makefile | 2 +-
drivers/nvmem/core.c | 288 +++++++++++---------
drivers/nvmem/internals.h | 58 ++++
drivers/nvmem/layouts.c | 201 ++++++++++++++
drivers/nvmem/layouts/onie-tlv.c | 36 ++-
drivers/nvmem/layouts/sl28vpd.c | 36 ++-
drivers/of/device.c | 41 +++
drivers/of/platform.c | 40 ---
include/linux/nvmem-consumer.h | 7 -
include/linux/nvmem-provider.h | 39 ++-
include/linux/of_device.h | 6 +
12 files changed, 581 insertions(+), 194 deletions(-)
create mode 100644 Documentation/ABI/testing/sysfs-nvmem-cells
create mode 100644 drivers/nvmem/internals.h
create mode 100644 drivers/nvmem/layouts.c

--
2.34.1