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

[Biju Das]

Hi Maxime,

> -----Original Message-----
> From: Maxime Ripard <mripard at kernel.org>
> Sent: Monday, July 8, 2024 9:54 AM
> Subject: Re: [PATCH] drm: renesas: shmobile: shmo_drm_crtc: Fix PM imbalance if RPM_ACTIVE is true
> 
> Hi,
> 
> 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>
> > ---
> >  drivers/gpu/drm/renesas/shmobile/shmob_drm_crtc.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/renesas/shmobile/shmob_drm_crtc.c
> > b/drivers/gpu/drm/renesas/shmobile/shmob_drm_crtc.c
> > index 2e2f37b9d0a4..42a5d6876bec 100644
> > --- 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.

Cheers,
Biju