Wolfram Sang [off-list ref] writes:

Removing attach_adapter from this driver caused a regression for at
least some machines. Those machines had the sensors described in their
DT, too, so they didn't need manual creation of the sensor devices. The
old code worked, though, because manual creation came first. Creation of
DT devices then failed later and caused error logs, but the sensors
worked nonetheless because of the manually created devices.

When removing attach_adaper, manual creation now comes later and loses
the race. The sensor devices were already registered via DT, yet with
another binding, so the driver could not be bound to it.

This fix refactors the code to remove the race and only manually creates
devices if there are no DT nodes present. Also, the DT binding is updated
to match both, the DT and manually created devices. Because we don't
know which device creation will be used at runtime, the code to start
the kthread is moved to do_probe() which will be called by both methods.

Fixes: 3e7bed52719d ("macintosh: therm_windtunnel: drop using attach_adapter")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=201723
Reported-by: Erhard Furtner <redacted>
Tested-by: Erhard Furtner <redacted>
Signed-off-by: Wolfram Sang <redacted>
---

I suggest this stable-tag: # v4.19+

Looks right to me.

Adding the Debian-PPC List to reach further people maybe willing to
test.

This patch does not depend on "[PATCH RESEND] macintosh: convert to
i2c_new_scanned_device". In fact, this one here should go in first as
5.6 material. I will rebase and resend the i2c_new_scanned_device()
conversion on top of this regression fix.

I can also take this via I2C if easier.

I think that would be best, it's more I2C related than powerpc arch
stuff that I could review.

I don't have a machine setup to test this easily, but Erhard has been
doing a good job of testing things so I'm happy for you to take it with
his Tested-by.

Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)

cheers