Re: [PATCH v1] PM: sleep: core: Synchronize runtime PM status of parents and children

Ulf Hansson
2025-01-29T11:53:27Z

On Tue, 28 Jan 2025 at 20:24, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
>
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>
> Commit 6e176bf8d461 ("PM: sleep: core: Do not skip callbacks in the
> resume phase") overlooked the case in which the parent of a device with
> DPM_FLAG_SMART_SUSPEND set did not use that flag and could be runtime-
> suspended before a transition into a system-wide sleep state. In that
> case, if the child is resumed during the subsequent transition from
> that state into the working state, its runtime PM status will be set to
> RPM_ACTIVE, but the runtime PM status of the parent will not be updated
> accordingly, even though the parent will be resumed too, because of the
> dev_pm_skip_suspend() check in device_resume_noirq().
>
> Address this problem by tracking the need to set the runtime PM status
> to RPM_ACTIVE during system-wide resume transitions for devices with
> DPM_FLAG_SMART_SUSPEND set and all of the devices depended on by them.
>
> Fixes: 6e176bf8d461 ("PM: sleep: core: Do not skip callbacks in the resume phase")
> Closes: https://lore.kernel.org/linux-pm/Z30p2Etwf3F2AUvD@hovoldconsulting.com/
> Reported-by: Johan Hovold <johan@kernel.org>
> Tested-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
> drivers/base/power/main.c | 29 ++++++++++++++++++++---------
> include/linux/pm.h | 1 +
> 2 files changed, 21 insertions(+), 9 deletions(-)
>
> --- a/drivers/base/power/main.c
> +++ b/drivers/base/power/main.c
> @@ -656,13 +656,15 @@
> * so change its status accordingly.
> *
> * Otherwise, the device is going to be resumed, so set its PM-runtime
> - * status to "active", but do that only if DPM_FLAG_SMART_SUSPEND is set
> - * to avoid confusing drivers that don't use it.
> + * status to "active" unless its power.set_active flag is clear, in
> + * which case it is not necessary to update its PM-runtime status.
> */
> - if (skip_resume)
> + if (skip_resume) {
> pm_runtime_set_suspended(dev);
> - else if (dev_pm_skip_suspend(dev))
> + } else if (dev->power.set_active) {
> pm_runtime_set_active(dev);
> + dev->power.set_active = false;
> + }
>
> if (dev->pm_domain) {
> info = "noirq power domain ";
> @@ -1189,18 +1191,24 @@
> return PMSG_ON;
> }
>
> -static void dpm_superior_set_must_resume(struct device *dev)
> +static void dpm_superior_set_must_resume(struct device *dev, bool set_active)
> {
> struct device_link *link;
> int idx;
>
> - if (dev->parent)
> + if (dev->parent) {
> dev->parent->power.must_resume = true;
> + if (set_active)
> + dev->parent->power.set_active = true;
> + }
>
> idx = device_links_read_lock();
>
> - list_for_each_entry_rcu_locked(link, &dev->links.suppliers, c_node)
> + list_for_each_entry_rcu_locked(link, &dev->links.suppliers, c_node) {
> link->supplier->power.must_resume = true;
> + if (set_active)
> + link->supplier->power.set_active = true;

If I understand correctly, the suppliers are already handled when the
pm_runtime_set_active() is called for consumers, so the above should
not be needed.

That said, maybe we instead allow parent/child to work in the similar
way as for consumer/suppliers, when pm_runtime_set_active() is called
for the child. In other words, when pm_runtime_set_active() is called
for a child and the parent is runtime PM enabled, let's runtime resume
it too, as we do for suppliers. Would that work, you think?

> + }
>
> device_links_read_unlock(idx);
> }
> @@ -1278,8 +1286,11 @@
> dev->power.may_skip_resume))
> dev->power.must_resume = true;
>
> - if (dev->power.must_resume)
> - dpm_superior_set_must_resume(dev);
> + if (dev->power.must_resume) {
> + dev->power.set_active = dev->power.set_active ||
> + dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_SUSPEND);
> + dpm_superior_set_must_resume(dev, dev->power.set_active);
> + }
>
> Complete:
> complete_all(&dev->power.completion);
> --- a/include/linux/pm.h
> +++ b/include/linux/pm.h
> @@ -683,6 +683,7 @@
> bool no_pm_callbacks:1; /* Owned by the PM core */
> bool async_in_progress:1; /* Owned by the PM core */
> bool must_resume:1; /* Owned by the PM core */
> + bool set_active:1; /* Owned by the PM core */
> bool may_skip_resume:1; /* Set by subsystems */
> #else
> bool should_wakeup:1;
>
>
>

Kind regards
Uffe