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

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Message-ID: <TY1PR01MB17697FBCBDC6296E7B2589C9F5510@TY1PR01MB1769.jpnprd01.prod.outlook.com>
Date:   Fri, 20 Jul 2018 12:26:00 +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 13:12, Geert Uytterhoeven wrote:
> On Fri, Jul 20, 2018 at 2:06 PM Phil Edworthy  wrote:
> > 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.
> 
> if the pinctrl driver uses subsys_initcall(), ...
> 
> > > > --- 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().
> 
> Hence they cannot have their probe function __init.
> 
> >
> > Thanks
> > Phil
> >
> > > > -subsys_initcall(r9a06g032_clocks_init);
> > > > +core_initcall(r9a06g032_clocks_init);
> 
> ... using postcore_initcall() or arch_initcall() here, should work with
> platform_driver_probe()?
Nope, you have to use platform_driver_register() for DT based drivers.
subsys_initcall is the earliest you can use platform_driver_probe().

Thanks
Phil

> 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