Message-ID: <2314745.iZASKD2KPV@rjwysocki.net>
Date: Tue, 11 Feb 2025 22:01:24 +0100
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Linux PM <linux-pm@...r.kernel.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
 Alan Stern <stern@...land.harvard.edu>, Ulf Hansson <ulf.hansson@...aro.org>,
 Johan Hovold <johan@...nel.org>,
 Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
 Jon Hunter <jonathanh@...dia.com>
Subject:
 [PATCH v1 00/10] PM: Make the core and pm_runtime_force_suspend/resume()
 agree more

Hi Everyone,

This series is a result of the discussion on a recently reported issue
with device runtime PM status propagation during system resume and
the resulting patches:

https://lore.kernel.org/linux-pm/12619233.O9o76ZdvQC@rjwysocki.net/
https://lore.kernel.org/linux-pm/6137505.lOV4Wx5bFT@rjwysocki.net/

Overall, due to restrictions related to pm_runtime_force_suspend() and
pm_runtime_force_resume(), it was necessary to limit the RPM_ACTIVE
setting propagation to the parent of the first device in a dependency
chain that turned out to have to be resumed during system resume even
though it was runtime-suspended before system suspend.

Those restrictions are that (1) pm_runtime_force_suspend() attempts to
suspend devices that have never had runtime PM enabled if their runtime
PM status is currently RPM_ACTIVE and (2) pm_runtime_force_resume()
will skip device whose runtime PM status is currently RPM_ACTIVE.

The purpose of this series is to eliminate the above restrictions and
get pm_runtime_force_suspend() and pm_runtime_force_resume() to agree
more with what the core does.

First off, it turns out that detecting devices that have never had
runtime PM enabled is not really hard - it is sufficient to check
their power.last_status data when runtime PM is disabled.  If
power.last_status is RPM_INVALID at that point, runtime PM has never
been enabled for the given device, so patch [01/10] adds a helper
function for checking that.

Patch [02/10] makes the PM core use the new function to avoid setting
power.set_active for devices with no runtime PM support which really
is a fixup on top of

https://lore.kernel.org/linux-pm/6137505.lOV4Wx5bFT@rjwysocki.net/

Patch [03/10] modifies pm_runtime_force_suspend() to skip devices
with no runtime PM support with the help of the new function.

Next, patch [04/10] uses the observation that the runtime PM status
check in pm_runtime_force_resume() is redundant and drops that check.

Patch [05/10] removes the wakeirq enabling from the pm_runtime_force_resume()
error path because it is not really a good idea to enable wakeirqs during
system resume.

Patch [06/10] makes the PM core somewhat more consistent with
pm_runtime_force_suspend() and patch [07/10] prepares it for the subsequent
changes.

Patch [08/10] changes pm_runtime_force_resume() to handle the case in
which the runtime PM status of the device has been updated by the core to
RPM_ACTIVE after pm_runtime_force_suspend() left it in RPM_SUSPENDED.

Patch [09/10] restores the RPM_ACTIVE setting propagation to parents
and suppliers, but it takes exceptions into account (for example, devices
with no runtime PM support).

Finally, patch [10/10] adds a mechanism to discover cases in which runtime PM
is disabled for a device permanently even though it has been enabled for that
device at one point.

Please have a look and let me know if you see any problems.

Thanks!

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