Re: [PATCH] PM: runtime: Simplify __rpm_get_callback()

From: Geert Uytterhoeven
Date: Tue Jan 24 2023 - 11:14:58 EST


Hi Bjorn,

On Tue, Jan 24, 2023 at 4:06 PM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
> On Tue, Jan 24, 2023 at 03:45:50PM +0100, Rafael J. Wysocki wrote:
> > On Tue, Jan 24, 2023 at 3:37 PM Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
> > > On Tue, Jan 24, 2023 at 3:18 PM Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote:
> > > > On Tue, Jan 24, 2023 at 12:20 PM Geert Uytterhoeven
> > > > <geert@xxxxxxxxxxxxxx> wrote:
> > > > > On Thu, Dec 15, 2022 at 7:23 PM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
> > > > > > From: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> > > > > >
> > > > > > Simplify __rpm_get_callback() slightly by returning as soon as the return
> > > > > > value is known. No functional change intended.
> > > > > >
> > > > > > Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> > > > >
> > > > > Thanks for your patch, which is now commit 650bdddb6b311705 ("PM:
> > > > > runtime: Simplify __rpm_get_callback()") in pm/linux-next.
> > > > >
> > > > > > --- a/drivers/base/power/runtime.c
> > > > > > +++ b/drivers/base/power/runtime.c
> > > > > > @@ -20,8 +20,7 @@ typedef int (*pm_callback_t)(struct device *);
> > > > > >
> > > > > > static pm_callback_t __rpm_get_callback(struct device *dev, size_t cb_offset)
> > > > > > {
> > > > > > - pm_callback_t cb;
> > > > > > - const struct dev_pm_ops *ops;
> > > > > > + const struct dev_pm_ops *ops = NULL;
> > > > > >
> > > > > > if (dev->pm_domain)
> > > > > > ops = &dev->pm_domain->ops;
> > > > > > @@ -31,18 +30,14 @@ static pm_callback_t __rpm_get_callback(struct device *dev, size_t cb_offset)
> > > > > > ops = dev->class->pm;
> > > > > > else if (dev->bus && dev->bus->pm)
> > > > > > ops = dev->bus->pm;
> > > > > > - else
> > > > > > - ops = NULL;
> > > > > >
> > > > > > if (ops)
> > > > > > - cb = *(pm_callback_t *)((void *)ops + cb_offset);
> > > > > > - else
> > > > > > - cb = NULL;
> > > > > > + return *(pm_callback_t *)((void *)ops + cb_offset);
> > > > >
> > > > > This is a change in behavior in case the callback turns out to be NULL:
> > > > > - before, it would fall back to the driver-specific callback below,
> > > > > - after, it always returns NULL.
> > > >
> > > > Good point and sorry for missing this!
> > > >
> > > > > >
> > > > > > - if (!cb && dev->driver && dev->driver->pm)
> > > > > > - cb = *(pm_callback_t *)((void *)dev->driver->pm + cb_offset);
> > > > > > + if (dev->driver && dev->driver->pm)
> > > > > > + return *(pm_callback_t *)((void *)dev->driver->pm + cb_offset);
> > > > > >
> > > > > > - return cb;
> > > > > > + return NULL;
> > > > > > }
> > > > >
> > > >
> > > > Something like the patch below (modulo gmail-induced whitespace
> > > > breakage) should restore the previous behavior if I'm not mistaken:
> > > >
> > > > ---
> > > > drivers/base/power/runtime.c | 9 +++++++--
> > > > 1 file changed, 7 insertions(+), 2 deletions(-)
> > > >
> > > > Index: linux-pm/drivers/base/power/runtime.c
> > > > ===================================================================
> > > > --- linux-pm.orig/drivers/base/power/runtime.c
> > > > +++ linux-pm/drivers/base/power/runtime.c
> > > > @@ -31,8 +31,13 @@ static pm_callback_t __rpm_get_callback(
> > > > else if (dev->bus && dev->bus->pm)
> > > > ops = dev->bus->pm;
> > > >
> > > > - if (ops)
> > > > - return *(pm_callback_t *)((void *)ops + cb_offset);
> > > > + if (ops) {
> > > > + pm_callback_t cb;
> > > > +
> > > > + cb = *(pm_callback_t *)((void *)ops + cb_offset);
> > > > + if (cb)
> > > > + return cb;
> > > > + }
> > > >
> > > > if (dev->driver && dev->driver->pm)
> > > > return *(pm_callback_t *)((void *)dev->driver->pm + cb_offset);
> > >
> > > Which is now more complex than the original?
> >
> > Arguably so.
> >
> > OK, I'll drop the commit in question then, sorry Bjorn.
>
> Really sorry about this. Think I'm all out of brown paper bags :(
> Thanks for catching this, Geert, and sorry for all the time you had to

Np, no time was wasted on debugging.
I just noticed because I have some local debug code on top, which no
longer applied 8^)

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds