Re: [PATCH 1/3] clk: renesas: mstp: Set GENPD_FLAG_ALWAYS_ON for clock domain

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Ulf,

On Thu, Aug 22, 2019 at 4:06 PM Ulf Hansson <ulf.hansson@linaro.org> wrote:
> > > Well is it actually a problem to not specify the flag? I guess it's just
> > > a potential problem if the genpd is ever powered off, but given that the
> > > governor decides to leave it always enabled it doesn't actually matter?
> > > So it's not really fixing anything besides silencing a harmless warning?
> >
> > The warning is indeed harmless.
> >
> > The "interesting" case is the case where no warning is printed, as no
> > IRQ-safe device is present.  In that case, the absence of the
> > GENPD_FLAG_ALWAYS_ON flag means that the core PM Domain code will
> > consider the domain for power-off, and will loop over all devices part
> > of it, which is suboptimal.  Setting the flag avoids that.
> >
> > Thanks for your continued questions, it made me realize I need to add more
> > meat to the description to these "simple" patches!
> >
> > For the PM people: would it make sense to add a
> > WARN(!genpd->power_off && !genpd_is_always_on(genpd), "...") check to
> > pm_genpd_init()?
> > Or set GENPD_FLAG_ALWAYS_ON automatically if !genpd->power_off?
>
> Well, wouldn't it be possible that the power is provided through a
> master domain, thus not having the ->power_off() callback assigned for
> the subdomain is perfectly fine, even without having
> GENPD_FLAG_ALWAYS_ON not set.

Thanks, I hadn't considered that the clock domain might be a subdomain
of a power domain.

Gr{oetje,eeting}s,

                        Geert

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