linux-kernel - Re: [PATCH v1 1/3] PM: runtime: Introduce PM_RUNTIME_ACQUIRE_OR

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Message-ID: <CAJZ5v0iWq=1HDHnj6_rTiK83cFiVyNimuSpLc5dYU9Tz90nqXw@mail.gmail.com>
Date: Thu, 16 Oct 2025 18:06:29 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Takashi Iwai <tiwai@...e.de>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Jonathan Cameron <jonathan.cameron@...wei.com>, 
	Linux PM <linux-pm@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, 
	Linux PCI <linux-pci@...r.kernel.org>, Alex Williamson <alex.williamson@...hat.com>, 
	Bjorn Helgaas <helgaas@...nel.org>, Zhang Qilong <zhangqilong3@...wei.com>, 
	Ulf Hansson <ulf.hansson@...aro.org>, Frank Li <Frank.Li@....com>, Dhruva Gole <d-gole@...com>, 
	Mika Westerberg <mika.westerberg@...ux.intel.com>, Linux ACPI <linux-acpi@...r.kernel.org>, 
	Dan Williams <dan.j.williams@...el.com>, David Lechner <dlechner@...libre.com>, 
	"Fabio M. De Francesco" <fabio.maria.de.francesco@...ux.intel.com>
Subject: Re: [PATCH v1 1/3] PM: runtime: Introduce PM_RUNTIME_ACQUIRE_OR_FAIL()
 macro

On Thu, Oct 16, 2025 at 4:59 PM Takashi Iwai <tiwai@...e.de> wrote:
>
> On Thu, 16 Oct 2025 15:46:08 +0200,
> Rafael J. Wysocki wrote:
> >
> > On Thu, Oct 16, 2025 at 2:39 PM Jonathan Cameron
> > <jonathan.cameron@...wei.com> wrote:
> > >
> > > On Wed, 15 Oct 2025 16:02:02 +0200
> > > "Rafael J. Wysocki" <rafael@...nel.org> wrote:
> > >
> > > > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > > >
> > > > There appears to be an emerging pattern in which guard
> > > > pm_runtime_active_try is used for resuming the given device and
> > > > incrementing its runtime PM usage counter if the resume has been
> > > > successful, that is followed by an ACQUIRE_ERR() check on the guard
> > > > variable and if that triggers, a specific error code is returned, for
> > > > example:
> > > >
> > > >       ACQUIRE(pm_runtime_active_try, pm)(dev);
> > > >       if (ACQUIRE_ERR(pm_runtime_active_try, &pm))
> > > >               return -ENXIO
> > > >
> > > > Introduce a macro called PM_RUNTIME_ACQUIRE_OR_FAIL() representing the
> > > > above sequence of statements that can be used to avoid code duplication
> > > > wherever that sequence would be used.
> > > >
> > > > Use this macro right away in the PCI sysfs code where the above pattern
> > > > is already present.
> > > >
> > > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > > > ---
> > > >
> > > > Admittedly, the new macro is slightly on the edge, but it really helps
> > > > reduce code duplication, so here it goes.
> > >
> > > Fully agree with the 'on the edge'.
> > >
> > > This looks somewhat like the some of the earlier attempts to come up with
> > > a general solution before ACQUIRE().  Linus was fairly clear on his opinion of
> > > a proposal that looked a bit similar to this
> > > cond_guard(mutex_intr, return -EINTR, &mutex);
> > >
> > > https://lore.kernel.org/all/CAHk-=win7bwWhPJ=iuW4h-sDTqbX6v9_LJnMaO3KxVfPSs81bQ@mail.gmail.com/
> > >
> > > +CC a few people who might have better memories of where things went than I do.
> > >
> > > The solution you have here has the benefit of clarity that all it can do is
> > > return the error code.
> >
> > Well, I could call the macro PM_RUNTIME_ACQUIRE_OR_RETURN_ERROR(), but
> > FAIL is just shorter. :-)
> >
> > Seriously though, the odd syntax bothers me, but it has come from
> > looking at the multiple pieces of code that otherwise would have
> > repeated exactly the same code pattern including the guard name in two
> > places and the pm variable that has no role beyond guarding.
>
> While I see the benefit of simplification, IMO, embedding a code
> flow control inside the macro argument makes it really harder to
> follow.
>
> Is the problem about the messy ACQUIRE_ERR() invocation?  If so, it
> could be replaced with something shorter (and without extra type),
> e.g. replace
>         ret = ACQUIRE_ERR(pm_runtime_active_try, &pm);
> with
>         ret = PM_RUNTIME_ACQUIRE_ERR(&pm);
>
> Since all runtime PM guard usage is to the same object, we can have a
> common macro.

Well, it's not a problem, but an observation that the code pattern is
exactly the same in all of the places that use this macro, so it
represents this exact same code pattern that otherwise will be
repeated in multiple places.

I have no problem with copy-pasting this code pattern between
different use sites, but that's something we generally avoid as a
rule, don't we?