[PATCH 0/5] PM: runtime: Improve autosuspend child to parent propagation

[Brian Norris <briannorris@chromium.org>]

See patch 3 for the primary change here.

In short: today, children can resume/suspend without extending the
autosuspend expiration of their parent. For parents where their activity
is largely driven by their children, this makes it easy to experience
"premature" suspend.

Many .runtime_idle() implementations seem to try to work around this
problem, and one in particular (stm32-adc) documented their problems
heavily in c537d3457542 ("iio: adc: stm32-adc: fix runtime autosuspend
delay when slow polling").

This is an attempt to improve the PM core, as suggested in review for that
change:
https://lore.kernel.org/all/CAPDyKFp=KTf8=zGBSzPYqhjnZpY8xwvjCeM1e-WTKT1QLSxaDA@mail.gmail.com/

This will make it easier to simplify many other drivers too, as a
significant use of .runtime_idle() is to simply extend a parent's
last_busy timestamp, as a proxy for "last activity performed by a
child".

The changes:

1) Preparatory fix, noticed while making the following changes

2) Because the last_busy mathematics get a little more complex, I have
   to change last_busy to use an atomic64_t type

3) Propagate last_busy from dependent devices (children, consumers) to
   their dependencies (parent, suppliers)

4) Add KUnit tests

5) Remove the pm_runtime_mark_last_busy() workaround from the stm32-adc
   driver

To follow on with #5: I believe almost every other .runtime_idle()
implementation in the tree can be removed after patch 3. (There are a
handful of drivers that should just use autosuspend. And perhaps 2 or 3
other drivers that do other non-trivial work with .runtime_idle(). But
most are redundant.) I may work on that next, if this works out.

- Brian


Brian Norris (5):
  PM: runtime: Only queue an idle check for RPM-linked suppliers (part
    2)
  PM: runtime: Convert last_busy to atomic64_t
  PM: runtime: Propagate last_busy from dependent to dependency
  PM: runtime: Add tests for last_busy propagation
  iio: adc: stm32-adc: Drop runtime_idle()

 drivers/base/power/runtime-test.c | 101 ++++++++++++++++++++++++++++++
 drivers/base/power/runtime.c      |  29 ++++++++-
 drivers/iio/adc/stm32-adc-core.c  |   9 +--
 include/linux/pm.h                |   3 +-
 include/linux/pm_runtime.h        |   2 +-
 5 files changed, 132 insertions(+), 12 deletions(-)

-- 
2.56.0.rc1.315.gc6ed9934b7-goog