linux-kernel - Re: [PATCH] nubus: Unconditionally register bus type

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Message-ID: <CAMuHMdUCEc0n1R6-=8fcw2xng7ETPUEs86PhC_0=1jY_AYV6Bg@mail.gmail.com>
Date:   Tue, 8 May 2018 08:32:22 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Finn Thain <fthain@...egraphics.com.au>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] nubus: Unconditionally register bus type

Hi Finn,

On Tue, May 8, 2018 at 1:44 AM, Finn Thain <fthain@...egraphics.com.au> wrote:
> On Mon, 7 May 2018, I 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) ||
>>
>
> That rushed example I gave above seems to be confusing the issue. Sorry
> about that. (See sioux-core.c for the code that motivated it.)
>
> This example is the sort of flag removal that I had in mind --
>
> diff --git a/drivers/base/driver.c b/drivers/base/driver.c
> index ba912558a510..4ee22fb3db92 100644
> --- a/drivers/base/driver.c
> +++ b/drivers/base/driver.c
> @@ -148,7 +148,8 @@ int driver_register(struct device_driver *drv)
>         int ret;
>         struct device_driver *other;
>
> -       BUG_ON(!drv->bus->p);
> +       if (!drv->bus->p)
> +               return -ENODEV;

If this is meant to handle the case where the device driver is registered
before the bus is registered, while the latter can still happen later,
then you want to return -EPROBE_DEFER.

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