Re: [PATCH 3/5] driver core: async device shutdown infrastructure

[David Jeffery]

On Wed, Mar 11, 2026 at 7:05 PM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
>
> On Wed, Mar 11, 2026 at 01:12:07PM -0400, David Jeffery wrote:
> > Patterned after async suspend, allow devices to mark themselves as wanting
> > to perform async shutdown. Devices using async shutdown wait only for their
> > dependencies to shutdown before executing their shutdown routine.
>
> I'm not an expert on dependencies.  Is it obvious to everybody else
> how these dependencies are expressed?  What would I look at to verify
> that, for example, PCI devices are dependencies of the PCI bridges
> leading to them?  I suppose it's the same dependencies used for
> suspend?

Yes, it uses the same dependencies as async suspend does.

> From wait_for_shutdown_dependencies() below, it looks like we'll wait
> for each child of dev and then wait for each consumer of dev before
> shutting down dev itself.

Right, just like async suspend, all children and consumers need to
shut down first for async shutdown.

>
> > Sync shutdown devices are shut down one at a time and will only wait for an
> > async shutdown device if the async device is a dependency.
>
> > @@ -132,6 +133,7 @@ struct device_private {
> >  #ifdef CONFIG_RUST
> >       struct driver_type driver_type;
> >  #endif
> > +     struct completion complete;
>
> I thought "complete" might be a little too generic, but I guess async
> suspend uses "dev->power.completion" :)

I am open to a better name, but anything I came up with ended up
excessively long in my opinion, so I settled on the current and boring
"complete".

>
> > +static void wait_for_shutdown_dependencies(struct device *dev, bool async)
> > +{
> > +     struct device_link *link;
> > +     int idx;
> > +
> > +     device_for_each_child(dev, &async, wait_for_device_shutdown);
> > +
> > +     idx = device_links_read_lock();
> > +
> > +     dev_for_each_link_to_consumer(link, dev)
> > +             if (!device_link_flag_is_sync_state_only(link->flags))
> > +                     wait_for_device_shutdown(link->consumer, &async);
> > +
> > +     device_links_read_unlock(idx);
> > +}
>
> > @@ -4828,6 +4919,12 @@ void device_shutdown(void)
> >
> >       cpufreq_suspend();
> >
> > +     /*
> > +      * Start async device threads where possible to maximize potential
> > +      * paralellism and minimize false dependency on unrelated sync devices
>
> s/paralellism/parallelism/
>

Gah, I will correct it.

David Jeffery