linux-kernel - Re: [PATCH v1 15/23] phy: core: Discard pm_runtime

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Message-ID: <CAMuHMdWshJOjzD5DGzyRUG66jvPC6PPVBgaT=UdWy+XOk_T5Pw@mail.gmail.com>
Date: Tue, 30 Dec 2025 11:54:17 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: Linux PM <linux-pm@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, 
	Ulf Hansson <ulf.hansson@...aro.org>, Brian Norris <briannorris@...omium.org>, 
	Vinod Koul <vkoul@...nel.org>, Neil Armstrong <neil.armstrong@...aro.org>, 
	linux-phy@...ts.infradead.org, 
	Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH v1 15/23] phy: core: Discard pm_runtime_put() return values

On Tue, 30 Dec 2025 at 11:34, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> On Mon, 22 Dec 2025 at 21:40, Rafael J. Wysocki <rafael@...nel.org> wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> >
> > The PHY core defines phy_pm_runtime_put() to return an int, but that
> > return value is never used.  It also passes the return value of
> > pm_runtime_put() to the caller which is not very useful.
> >
> > Returning an error code from pm_runtime_put() merely means that it has
> > not queued up a work item to check whether or not the device can be
> > suspended and there are many perfectly valid situations in which that
> > can happen, like after writing "on" to the devices' runtime PM "control"
> > attribute in sysfs for one example.
> >
> > Modify phy_pm_runtime_put() to discard the pm_runtime_put() return
> > value and change its return type to void.  Also drop the redundant
> > pm_runtime_enabled() call from there.
> >
> > No intentional functional impact.
> >
> > This will facilitate a planned change of the pm_runtime_put() return
> > type to void in the future.
> >
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>
> Thanks for your patch, which is now commit caad07ae07e3fb17 ("phy:
> core: Discard pm_runtime_put() return values") in phy/next.
>
> This is causing several messages like
>
>     phy phy-e6590100.usb-phy-controller.2: Runtime PM usage count underflow!
>
> during boot, and s2ram on Koelsch (R-Car M2-W).

On R-Car Gen3, there are no such messages, as e.g.
drivers/phy/renesas/phy-rcar-gen3-usb2.c does support Runtime PM.
R-Car Gen2 uses drivers/phy/renesas/phy-rcar-gen2.c, which does not
use Runtime PM yet, but still relies on explicit clock management.

> > --- a/drivers/phy/phy-core.c
> > +++ b/drivers/phy/phy-core.c
> > @@ -190,15 +190,12 @@ int phy_pm_runtime_get_sync(struct phy *
> >  }
> >  EXPORT_SYMBOL_GPL(phy_pm_runtime_get_sync);
> >
> > -int phy_pm_runtime_put(struct phy *phy)
> > +void phy_pm_runtime_put(struct phy *phy)
> >  {
> >         if (!phy)
> > -               return 0;
> > +               return;
> >
> > -       if (!pm_runtime_enabled(&phy->dev))
> > -               return -ENOTSUPP;
>
> Adding some instrumentation shows that this branch was taken before,
> thus skipping the call to pm_runtime_put().
>
> Can I just put the check back, or is there an underlying problem that
> should be fixed instead?

I assume the PHY core should support both drivers that do and do not
support Runtime PM.

> Thanks!
>
> > -
> > -       return pm_runtime_put(&phy->dev);
> > +       pm_runtime_put(&phy->dev);
> >  }
> >  EXPORT_SYMBOL_GPL(phy_pm_runtime_put);

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

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