Re: [PATCH 8/8] net/iucv: Use the new device_to_pm() helper to access struct dev_pm_ops

Rafael J. Wysocki
2020-05-26T16:06:41Z

On Tue, May 26, 2020 at 5:28 PM Alan Stern <stern@rowland.harvard.edu> wrote:
>
> On Tue, May 26, 2020 at 05:19:07PM +0200, Rafael J. Wysocki wrote:
> > On Tue, May 26, 2020 at 5:07 PM Krzysztof Wilczyński <kw@linux.com> wrote:
> > >
> > > Hello Greg,
> > >
> > > [...]
> > > > It's "interesting" how using your new helper doesn't actually make the
> > > > code smaller. Perhaps it isn't a good helper function?
> > >
> > > The idea for the helper was inspired by the comment Dan made to Bjorn
> > > about Bjorn's change, as per:
> > >
> > > https://lore.kernel.org/driverdev-devel/20191016135002.GA24678@kadam/
> > >
> > > It looked like a good idea to try to reduce the following:
> > >
> > > dev->driver && dev->driver->pm && dev->driver->pm->prepare
> > >
> > > Into something more succinct. Albeit, given the feedback from yourself
> > > and Rafael, I gather that this helper is not really a good addition.
> >
> > IMO it could be used for reducing code duplication like you did in the
> > PCI code, but not necessarily in the other places where the code in
> > question is not exactly duplicated.
>
> The code could be a little more succinct, although it wouldn't fit every
> usage. For example,
>
> #define pm_do_callback(dev, method) \
> (dev->driver && dev->driver->pm && dev->driver->pm->callback ? \
> dev->driver->pm->callback(dev) : 0)
>
> Then the usage is something like:
>
> ret = pm_do_callback(dev, prepare);
>
> Would this be an overall improvement?

It wouldn't cover all of the use cases.

For example, PCI does other things in addition to running a callback
when it is present.

Something like this might be enough though:

#define pm_driver_callback_is_present(dev, method) \
(dev->driver && dev->driver->pm && dev->driver->pm->method)

#define pm_run_driver_callback(dev, method) \
(pm_driver_callback_is_present(dev, method) ?
dev->driver->pm->method(dev) : 0)

#define pm_get_driver_callback(dev, method) \
(pm_driver_callback_is_present(dev, method) ?
dev->driver->pm->method : NULL)

so whoever needs the callback pointer can use pm_get_driver_callback()
and whoever only needs to run the callback can use
pm_run_driver_callback().

Cheers!