linux-kernel - Re: [PATCH v4 1/3] pmdomain: core: introduce dev_pm_genpd_is

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Message-ID: <CAPDyKFoHHMv1MUnT-ZUTDiwZdMChq1KooQxnNDx=eettpoTAGA@mail.gmail.com>
Date: Mon, 16 Jun 2025 15:13:26 +0200
From: Ulf Hansson <ulf.hansson@...aro.org>
To: Hiago De Franco <hiagofranco@...il.com>
Cc: Bjorn Andersson <andersson@...nel.org>, Mathieu Poirier <mathieu.poirier@...aro.org>, 
	linux-pm@...r.kernel.org, linux-remoteproc@...r.kernel.org, 
	Shawn Guo <shawnguo@...nel.org>, Sascha Hauer <s.hauer@...gutronix.de>, 
	Hiago De Franco <hiago.franco@...adex.com>, imx@...ts.linux.dev, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	Peng Fan <peng.fan@....nxp.com>, daniel.baluta@....com, iuliana.prodan@....nxp.com, 
	"Rafael J . Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH v4 1/3] pmdomain: core: introduce dev_pm_genpd_is_on

On Thu, 12 Jun 2025 at 19:31, Hiago De Franco <hiagofranco@...il.com> wrote:
>
> On Wed, Jun 11, 2025 at 10:32:28AM -0500, Bjorn Andersson wrote:
> > On Mon, Jun 02, 2025 at 10:19:03AM -0300, Hiago De Franco wrote:
> > > From: Hiago De Franco <hiago.franco@...adex.com>
> > >
> > > This helper function returns the current power status of a given generic
> > > power domain.
> > >
> >
> > Please correct me if I'm wrong, but this returns the momentary status of
> > the device's associated genpd, and as genpds can be shared among devices
> > wouldn't there be a risk that you think the genpd is on but then that
> > other device powers it off?
>
> I am not fully familiar with the genpd's, so my knowledge might be
> limited, but I think this is correct, if the genpd is shared.
>
> >
> > > As example, remoteproc/imx_rproc.c can now use this function to check
> > > the power status of the remote core to properly set "attached" or
> > > "offline" modes.
> >
> > I presume this example works because there is a dedicated, single usage,
> > genpd for the remoteproc instance?
>
> Peng might correct if I am wrong, but yes, I believe this is correct.
>
> >
> > >
> > > Suggested-by: Ulf Hansson <ulf.hansson@...aro.org>
> > > Signed-off-by: Hiago De Franco <hiago.franco@...adex.com>
> > > ---
> > > v4: New patch.
> > > ---
> > >  drivers/pmdomain/core.c   | 27 +++++++++++++++++++++++++++
> > >  include/linux/pm_domain.h |  6 ++++++
> > >  2 files changed, 33 insertions(+)
> > >
> > > diff --git a/drivers/pmdomain/core.c b/drivers/pmdomain/core.c
> > > index ff5c7f2b69ce..bcb74d10960c 100644
> > > --- a/drivers/pmdomain/core.c
> > > +++ b/drivers/pmdomain/core.c
> > > @@ -758,6 +758,33 @@ int dev_pm_genpd_rpm_always_on(struct device *dev, bool on)
> > >  }
> > >  EXPORT_SYMBOL_GPL(dev_pm_genpd_rpm_always_on);
> > >
> > > +/**
> > > + * dev_pm_genpd_is_on - Get device's power status
> >
> > Functions in kernel-doc should have () prefix
>
> Thanks, I will correct this is next patch version.
>
> >
> > > + *
> > > + * @dev: Device to get the current power status
> > > + *
> > > + * This function checks whether the generic power domain is on or not by
> > > + * verifying if genpd_status_on equals GENPD_STATE_ON.
> > > + *
> >
> > If my understanding is correct, I'd like a warning here saying that this
> > is dangerous if the underlying genpd is shared.
>
> I believe this is correct, maybe Peng or Ulf can also comment here, but
> if that is the case then I can update the comment.

Good point!

I would not say that it's "dangerous", while I agree that we need to
extend the comment to make it really clear that it returns the current
power status of the genpd, which potentially may change beyond
returning from the function and especially if the genpd has multiple
consumers.

[...]

Kind regards
Uffe