On Tue, Feb 18, 2025 at 11:20 PM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
>
> On Tue, Feb 18, 2025 at 09:16:48PM +0100, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> >
> > A recent discussion has revealed that using DPM_FLAG_SMART_SUSPEND
> > unconditionally is generally problematic because it may lead to
> > situations in which the device's runtime PM information is internally
> > inconsistent or does not reflect its real state [1].
> >
> > For this reason, change the handling of DPM_FLAG_SMART_SUSPEND so that
> > it is only taken into account if it is consistently set by the drivers
> > of all devices having any PM callbacks throughout dependency graphs in
> > accordance with the following rules:
> >
> > - The "smart suspend" feature is only enabled for devices whose drivers
> > ask for it (that is, set DPM_FLAG_SMART_SUSPEND) and for devices
> > without PM callbacks unless they have never had runtime PM enabled.
> >
> > - The "smart suspend" feature is not enabled for a device if it has not
> > been enabled for the device's parent unless the parent does not take
> > children into account or it has never had runtime PM enabled.
> >
> > - The "smart suspend" feature is not enabled for a device if it has not
> > been enabled for one of the device's suppliers taking runtime PM into
> > account unless that supplier has never had runtime PM enabled.
> >
> > Namely, introduce a new device PM flag called smart_suspend that is only
> > set if the above conditions are met and update all DPM_FLAG_SMART_SUSPEND
> > users to check power.smart_suspend instead of directly checking the
> > latter.
> >
> > At the same time, drop the power.set_active flage introduced recently
> > in commit 3775fc538f53 ("PM: sleep: core: Synchronize runtime PM status
> > of parents and children") because it is now sufficient to check
> > power.smart_suspend along with the dev_pm_skip_resume() return value
> > to decide whether or not pm_runtime_set_active() needs to be called
> > for the device.
> >
> > Link: https://lore.kernel.org/linux-pm/CAPDyKFroyU3YDSfw_Y6k3giVfajg3NQGwNWeteJWqpW29BojhQ@xxxxxxxxxxxxxx/ [1]
> > Fixes: 7585946243d6 ("PM: sleep: core: Restrict power.set_active propagation")
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> > Reviewed-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
>
> Acked-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx> # drivers/pci
Thanks!
