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

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Date:   Sun, 6 May 2018 16:00:15 +1000 (AEST)
From:   Finn Thain <fthain@...egraphics.com.au>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-m68k@...ts.linux-m68k.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nubus: Unconditionally register bus type

On Sat, 5 May 2018, Greg Kroah-Hartman wrote:

> On Sun, May 06, 2018 at 11:47:52AM +1000, Finn Thain wrote:
> > Loading a NuBus driver module on a non-NuBus machine triggers the
> > BUG_ON(!drv->bus->p) in driver_register() because the bus does not get
> > registered unless MACH_IS_MAC(). Avoid this by registering the bus
> > unconditionally using postcore_initcall().
> > 
> > Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > Reported-by: Michael Schmitz <schmitzmic@...il.com>
> > Tested-by: Stan Johnson <userm57@...oo.com>
> > Fixes: 7f86c765a6a2 ("nubus: Add support for the driver model")
> > Signed-off-by: Finn Thain <fthain@...egraphics.com.au>
> > ---
> >  drivers/nubus/bus.c   | 3 ++-
> >  drivers/nubus/nubus.c | 5 -----
> >  include/linux/nubus.h | 1 -
> >  3 files changed, 2 insertions(+), 7 deletions(-)
> > 
> > diff --git a/drivers/nubus/bus.c b/drivers/nubus/bus.c
> > index d306c348c857..27ca9f1a281b 100644
> > --- a/drivers/nubus/bus.c
> > +++ b/drivers/nubus/bus.c
> > @@ -63,7 +63,7 @@ static struct device nubus_parent = {
> >  	.init_name	= "nubus",
> >  };
> >  
> > -int __init nubus_bus_register(void)
> > +static int __init nubus_bus_register(void)
> >  {
> >  	int err;
> >  
> > @@ -78,6 +78,7 @@ int __init nubus_bus_register(void)
> >  	device_unregister(&nubus_parent);
> >  	return err;
> >  }
> > +postcore_initcall(nubus_bus_register);
> 
> 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 found a few drivers that set a flag the way you describe, which could 
then be simplified.

But that pattern is rare. Most buses use the postcore_initcall() pattern, 
and so my patch took the conventional approach.

> And then fix your linking error, the bus should come first in link 
> order, before your drivers :)
> 

I didn't encounter any errors. How shall I reproduce this?

Thanks.

-- 

> thanks,
> 
> greg k-h