[PATCH] drm: renesas: shmobile: shmo_drm_crtc: Fix PM imbalance if RPM_ACTIVE is true

[Geert Uytterhoeven]

Hi Biju,

On Mon, Jul 8, 2024 at 11:00 AM Biju Das <biju.das.jz at bp.renesas.com> wrote:
> > From: Maxime Ripard <mripard at kernel.org>
> > On Mon, Jul 08, 2024 at 09:27:09AM GMT, Biju Das wrote:
> > > The pm_runtime_resume_and_get() returns 1 if RPM is active, in this
> > > case it won't call a put. This will result in PM imbalance as it treat
> > > this as an error and propagate this to caller and the caller never
> > > calls corresponding put(). Fix this issue by checking error condition
> > > only.
> > >
> > > Signed-off-by: Biju Das <biju.das.jz at bp.renesas.com>

> > > --- a/drivers/gpu/drm/renesas/shmobile/shmob_drm_crtc.c
> > > +++ b/drivers/gpu/drm/renesas/shmobile/shmob_drm_crtc.c
> > > @@ -208,7 +208,7 @@ static void shmob_drm_crtc_atomic_enable(struct drm_crtc *crtc,
> > >     int ret;
> > >
> > >     ret = pm_runtime_resume_and_get(dev);
> > > -   if (ret)
> > > +   if (ret < 0)
> > >             return;
> >
> > The documentation of pm_runtime_resume_and_get says that:
> >
> >   Resume @dev synchronously and if that is successful, increment its
> >   runtime PM usage counter. Return 0 if the runtime PM usage counter of
> >   @dev has been incremented or a negative error code otherwise.
> >
> > So it looks like it can't return 1, ever. Are you sure you're not confusing pm_runtime_resume_and_get
> > with pm_runtime_get?
>
> It should be ret < 0 as ret = 1 corresponds to RPM_ACTIVE and the API does not call put() when ret = 1; see [1] and [2]
>
> [1] https://elixir.bootlin.com/linux/v6.10-rc6/source/drivers/base/power/runtime.c#L778
>
> [2] https://elixir.bootlin.com/linux/v6.10-rc6/source/include/linux/pm_runtime.h#L431
>
> Am I miss anything? Please let me know.

Thanks for your patch, but the code for pm_runtime_resume_and_get()
seems to disagree?
https://elixir.bootlin.com/linux/latest/source/include/linux/pm_runtime.h#L436

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-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