Re: [PATCH net-next v3 01/14] dpll: dpllsim: Add simulated DPLL device driver

[netdev-bot+sashiko@kernel.org]

Thank you for your contribution! Sashiko AI review found more severe
issue(s) in other patches of this series. This mail is only an FYI, in case
you want to address the nit picks below when you respin.

Low priority / nit picks for your consideration:

- [Low] The commit message says configfs was chosen partly because
  "Unlike sysfs, configfs does not imply a stable ABI, which suits a…

--

dpll: dpllsim: Add simulated DPLL device driver

This commit adds dpllsim, a driver that provides simulated DPLL devices
for testing the DPLL subsystem without real hardware. Userspace creates
instances through configfs under /sys/kernel/config/dpllsim/, sets a
clock_id and writes 1 to live to register the device with the DPLL core.
The device registers as a PPS type DPLL with only the mode_get and
lock_status_get callbacks.

> Keeping registration separate from creation lets a test register and
> unregister the same device repeatedly, which is where the core bugs the
> driver is meant to catch tend to live, and it allows the structural
> attributes to be refused with EBUSY while the device is visible to
> userspace. Unlike sysfs, configfs does not imply a stable ABI, which
> suits a driver whose knobs exist only to drive tests.

[Severity: Low]
Is this statement about configfs accurate?

The kernel has no ABI exemption for configfs. Its attributes are
user-visible interfaces and fall under the same no-regression rule as
sysfs.

The tree already documents configfs interfaces as ABI in:

  Documentation/ABI/testing/configfs-most
  Documentation/ABI/testing/configfs-thunderbolt_stream
  Documentation/ABI/testing/configfs-tsm-report

Neither Documentation/filesystems/configfs.rst nor Documentation/ABI/README
makes an exception for configfs.

The selftests in this series will use the layout added here,
/sys/kernel/config/dpllsim/<dev>/{clock_id,live}, which later patches extend
with pins/<pin>/{type,frequency,direction,prio}. External tooling may use it
too. After that, renaming or changing these attributes would break
userspace.

The layout is currently documented only in
Documentation/driver-api/dpllsim.rst. There is no Documentation/ABI entry
and no note saying the interface is unstable or for testing only.

Could the claim be dropped from the commit message, or the interface be
documented under Documentation/ABI/testing/?

-- 
Sashiko AI review · https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20261109093523.931201-1-poros%40redhat.com