Re: RFC: a failing pm_runtime_get increases the refcnt?

[Rafael J. Wysocki]

On Sun, Jun 14, 2020 at 11:08 AM Wolfram Sang <wsa@xxxxxxxxxx> wrote:
>
> Hi Linux-PM,
>
> both in the I2C subsystem and also for Renesas drivers I maintain, I am
> starting to get boilerplate patches doing some pm_runtime_put_* variant
> because a failing pm_runtime_get is supposed to increase the ref
> counters? Really?

Yes.  Really.

pm_runtime_get*() have been doing this forever, because the majority
of their users do something like

pm_runtime_get*()

...

pm_runtime_put*()

without checking the return values and they don't need to worry about
the refcounts, which wouldn't be possible otherwise.

> This feels wrong and unintuitive to me. I expect there
> has been a discussion around it but I couldn't find it. I wonder why we
> don't fix the code where the incremented refcount is expected for some
> reason.
>
> Can I have some pointers please?

The behavior is actually documented in
Documentation/power/runtime_pm.rst and I'm working on kerneldoc
comments for runtime PM functions in general to make it a bit more
clear.

Cheers!