[...]

Fourth & final question: I'm under the impression that pm runtime calls
be be nested and re-enter, but I want to make sure (Ulf?). For instance
it is highly likely that this new feature would cause something like:

pm_runtime_get()              - called by random driver
-> clk_prepare_enable()       - genpd enables functioal clocks
   -> pm_runtime_get()        - called by clk_pm_runtime_get in clk core
      -> clk_prepare_enable() - genpd enables interface or bus clocks

I guess this is safe from the pm_runtime_get/genpd perspective, but want
to make sure first.

I noticed Marek's reply, which perhaps is sufficient. However, to
clarify also from genpd and runtime PM point of view the re-entrant
issue is safe and it is already quite commonly used.

For example, from a random driver's ->runtime_resume() callback
clk_prepare_enable() is called. When such clock is managed behind a
i2c interface the i2c controller also needs to be runtime resumed,
meaning its driver calls pm_runtime_get_sync(), before it can serve
the request and ungate the clock.

[...]

Kind regards
Uffe