Re: [PATCH v4 2/2] PM: runtime: Add Example Driver Patterns section

[Rafael J. Wysocki (Intel)]

On Fri, Oct 16, 2026 at 7:42 PM Rafael J. Wysocki (Intel)
<rafael@xxxxxxxxxx> wrote:
> On Thu, Oct 15, 2026 at 10:55 PM Brian Norris <briannorris@xxxxxxxxxxxx> wrote:
> > On Thu, Oct 15, 2026 at 10:11:04PM +0200, Rafael J. Wysocki (Intel) wrote:
> > > On Wed, Oct 14, 2026 at 10:15 PM Brian Norris <briannorris@xxxxxxxxxxxx> wrote:
> > > > On Wed, Oct 14, 2026 at 09:07:54PM +0200, Rafael J. Wysocki (Intel) wrote:
> > > > > On Thu, Oct 1, 2026 at 5:51 PM Brian Norris <briannorris@xxxxxxxxxxxx> wrote:
> > > > > >

[cut]

> >
> > I kinda think the point of most of this power domain architecture is
> > that a typical driver just doesn't have to worry about it at all (in
> > probe(), and if you use runtime PM properly), so I'd prefer not
> > mentioning it in the Basic example. But sure.
>
> Well, your basic example needs to be put in a certain context because
> it may not be generally applicable everywhere.
>
> I think that you should make it clear what the driver's expectations
> regarding the physical state of the device at the probe time are and
> the general rule is that it is better to leave the device in the same
> state in which it is expected to be found next time.

To be somewhat more precise, if the driver expects to find the device
completely off and the runtime PM callbacks are set up to make it
operational, runtime PM can be used to power it up in probe:

/* Assume the runtime PM status to be "suspended". */
pm_runtime_enable(dev);
pm_runtime_get_sync(dev);

but then in remove or on probe errors the "power off" state needs to
be restored manually:

pm_runtime_disable(dev);
/* Allow the parent and suppliers (if any) to suspend. */
pm_runtime_set_suspended(dev);
device_specific_power_off(dev);

However, if the driver expects to find the device operational (for
example, because it assumes the ACPI PM domain to be there), it may
just update the runtime PM status before enabling runtime PM:

/* Assume the runtime PM status to be "suspended". */
pm_runtime_set_active(dev);
pm_runtime_enable(dev);

but then in remove or on probe errors it may just leave the device in
its current physical state (whatever it is) and assume somebody else
to take care of turning it off subsequently:

pm_runtime_disable(dev);
/* Allow the parent and suppliers (if any) to suspend. */
pm_runtime_set_suspended(dev);

These are two distinct cases that are rather hard to cover in one
simple example.