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SubjectRe: [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@linuxfoundation.org>
> > Reported-by: Michael Schmitz <schmitzmic@gmail.com>
> > Tested-by: Stan Johnson <userm57@yahoo.com>
> > Fixes: 7f86c765a6a2 ("nubus: Add support for the driver model")
> > Signed-off-by: Finn Thain <fthain@telegraphics.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

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