linux-kernel - Re: RFC: a failing pm_runtime

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Message-ID: <CAHp75VekhzjoGzKp2+fdsxhJOuUFanPz=LCC4JGWJwCqqPrfVw@mail.gmail.com>
Date:   Sun, 14 Jun 2020 15:42:07 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Wolfram Sang <wsa@...nel.org>, Linux PM <linux-pm@...r.kernel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-i2c <linux-i2c@...r.kernel.org>
Subject: Re: RFC: a failing pm_runtime_get increases the refcnt?

On Sun, Jun 14, 2020 at 1:00 PM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>
> Hi Andy,
>
> On Sun, Jun 14, 2020 at 11:43 AM Andy Shevchenko
> <andy.shevchenko@...il.com> wrote:
> > On Sun, Jun 14, 2020 at 12:34 PM Andy Shevchenko
> > <andy.shevchenko@...il.com> wrote:
> > >
> > > On Sun, Jun 14, 2020 at 12:10 PM Wolfram Sang <wsa@...nel.org> wrote:
> > > > both in the I2C subsystem and also for Renesas drivers I maintain, I am
> > > > starting to get boilerplate patches doing some pm_runtime_put_* variant
> > > > because a failing pm_runtime_get is supposed to increase the ref
> > > > counters? Really? This feels wrong and unintuitive to me.
> > >
> > > Yeah, that is a well known issue with PM (I even have for a long time
> > > a coccinelle script, when I realized myself that there are a lot of
> > > cases like this, but someone else discovered this recently, like
> > > opening a can of worms).
> > >
> > > > I expect there
> > > > has been a discussion around it but I couldn't find it.
> > >
> > > Rafael explained (again) recently this. I can't find it quickly, unfortunately.
> >
> > I _think_ this discussion, but may be it's simple another tentacle of
> > the same octopus.
> > https://patchwork.ozlabs.org/project/linux-tegra/patch/20200520095148.10995-1-dinghao.liu@zju.edu.cn/
>
> Thanks, hadn't read that one! (so I was still at -1 from
> http://sweng.the-davies.net/Home/rustys-api-design-manifesto ;-)

This one seems the starting point:

https://lkml.org/lkml/2020/5/20/1100

> So "pm_runtime_put_noidle()" is the (definitive?) one to pair with a
> pm_runtime_get_sync() failure?

Depends. If you are using autosuspend, then put_autosuspend() probably
is the right one.

> > > > I wonder why we
> > > > don't fix the code where the incremented refcount is expected for some
> > > > reason.
> > >
> > > The main idea behind API that a lot of drivers do *not* check error
> > > codes from runtime PM, so, we need to keep balance in case of
> > >
> > > pm_runtime_get(...);
> > > ...
> > > pm_runtime_put(...);
>
> I've always[*] considered a pm_runtime_get_sync() failure to be fatal
> (or: cannot happen), and that there's nothing that can be done to
> recover.  Hence I never checked the function's return value.
> Was that wrong?
>
> [*] at least on Renesas SoCs with Clock and/or Power Domains.
>
> 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



-- 
With Best Regards,
Andy Shevchenko