linux-kernel - RE: [PATCH] clk: renesas: r9a06g032: Avoid needless probe deferring

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Date:   Fri, 20 Jul 2018 12:06:48 +0000
From:   Phil Edworthy <phil.edworthy@...esas.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
CC:     Simon Horman <horms@...ge.net.au>,
        linux-clk <linux-clk@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: RE: [PATCH] clk: renesas: r9a06g032: Avoid needless probe deferring

Hi Geert,

On 20 July 2018 12:21, Geert Uytterhoeven wrote:
> On Wed, Jul 18, 2018 at 4:34 PM Phil Edworthy wrote:
> > To avoid all SoC peripheral drivers deferring their probes, both clock
> > and pinctrl drivers should already be probed. Since the pinctrl driver
> > requires a clock to access the registers, the clock driver should be
> > probed before the pinctrl driver.
> >
> > Therefore, move the clock driver from subsys_initcall to core_initcall.
> >
> > Signed-off-by: Phil Edworthy <phil.edworthy@...esas.com>
> 
> Thanks for your patch!
Thanks for your review!

> The (not yet upstreamed) pinctrl driver uses postcore_initcall(), right?
No, the pinctrl driver uses subsys_initcall, but postcore_initcall or 
arch_initcall may be better to make it clear about the dependencies.

> > --- a/drivers/clk/renesas/r9a06g032-clocks.c
> > +++ b/drivers/clk/renesas/r9a06g032-clocks.c
> > @@ -877,17 +877,18 @@ static const struct of_device_id
> r9a06g032_match[] = {
> >         { }
> >  };
> >
> > -static struct platform_driver r9a06g032_clock_driver = {
> > +static struct platform_driver r9a06g032_clock_driver __refdata = {
> >         .driver         = {
> >                 .name   = "renesas,r9a06g032-sysctrl",
> >                 .of_match_table = r9a06g032_match,
> >         },
> > +       .probe = r9a06g032_clocks_probe,
> >  };
> >
> >  static int __init r9a06g032_clocks_init(void)  {
> > -       return platform_driver_probe(&r9a06g032_clock_driver,
> > -                       r9a06g032_clocks_probe);
> > +       platform_driver_register(&r9a06g032_clock_driver);
> > +       return 0;
That should be:
+       return platform_driver_register(&r9a06g032_clock_driver);

> >  }
> 
> Why are all of the above changes needed?
> Shouldn't the platform_driver_probe() keep on working?
> If it does not, it means the clock driver has some other dependency, and
> cannot be bound immediately.  This is potentially a dangerous situation, as
> r9a06g032_clocks_probe() is __init, but can still be called at any time later.
> Hence using platform_driver_probe() is the safe thing to do, possibly with a
> different reshuffling of the clock and pinctrl initcall priorities.
No, you cannot call platform_driver_probe() from core_initcall.
All drivers that are in core_initcall call platform_driver_register().

Thanks
Phil

> > -subsys_initcall(r9a06g032_clocks_init);
> > +core_initcall(r9a06g032_clocks_init);
> 
> 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