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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Tue, 8 May 2018 08:28:37 +0200
Message-ID: <CAMuHMdUBdm-wQ-swoBCRLJT7-=qaF4oRG-i4Rvc+tctWpWD38Q@mail.gmail.com>
Subject: Re: [PATCH] nubus: Unconditionally register bus type
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Finn Thain <fthain@telegraphics.com.au>,
        linux-m68k <linux-m68k@lists.linux-m68k.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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Hi Greg,

On Mon, May 7, 2018 at 4:45 PM, Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
> On Mon, May 07, 2018 at 02:53:13PM +0200, Geert Uytterhoeven wrote:
>> On Mon, May 7, 2018 at 1:57 AM, Finn Thain <fthain@telegraphics.com.au> wrote:
>> > On Sun, 6 May 2018, Greg Kroah-Hartman wrote:
>> >> > > Why not just have an "bus is registered" flag in your driver
>> >> > > register function that refuses to let drivers register with the
>> >> > > driver core if it isn't set?
>> >> >
>> >> > Perhaps that should happen in the core driver_register() function.
>> >> > BUG_ON is frowned upon, after all. Would that be acceptable?
>> >>
>> >> I don't understand what you mean here, perhaps make a patch to show it?
>> >>
>> >
>> > As an alternative to your suggestion (add flag to avoid the BUG_ON):
>> >
>> > --- a/drivers/base/driver.c
>> > +++ b/drivers/base/driver.c
>> > @@ -148,7 +148,10 @@ int driver_register(struct device_driver *drv)
>> >         int ret;
>> >         struct device_driver *other;
>> >
>> > -       BUG_ON(!drv->bus->p);
>> > +       if (!drv->bus->p) {
>> > +               WARN_ONCE(1, "Cannot register driver with invalid bus\n");
>> > +               return -EPROBE_DEFER;
>> > +       }
>> >
>> >         if ((drv->bus->probe && drv->probe) ||
>> >             (drv->bus->remove && drv->remove) ||
>> >
>> > I'm not actually proposing this change; just responding to your question.
>>
>> The bus_type.p field may be unused by some bus drivers, hence this
>> would prevent their drivers from being registered.
>
> bus_type.p is an internal-to-the-driver-core structure, no bus driver
> should ever be touching it.  This is a catch to see if someone is using
> the driver core incorrectly.

Thanks, I stand corrected.

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