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Date:   Thu, 22 Jun 2023 09:53:26 +0200
From:   Simon Horman <simon.horman@corigine.com>
To:     Alexandra Winter <wintera@linux.ibm.com>
Cc:     Randy Dunlap <rdunlap@infradead.org>, linux-kernel@vger.kernel.org,
        kernel test robot <lkp@intel.com>,
        Wenjia Zhang <wenjia@linux.ibm.com>,
        linux-s390@vger.kernel.org, netdev@vger.kernel.org,
        Heiko Carstens <hca@linux.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Alexander Gordeev <agordeev@linux.ibm.com>,
        Christian Borntraeger <borntraeger@linux.ibm.com>,
        Sven Schnelle <svens@linux.ibm.com>,
        "David S . Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>
Subject: Re: [PATCH] s390/net: lcs: fix build errors when FDDI is a loadable
 module
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On Thu, Jun 22, 2023 at 09:15:24AM +0200, Alexandra Winter wrote:
> 
> 
> On 21.06.23 23:37, Randy Dunlap wrote:
> > Require FDDI to be built-in if it is used. LCS needs FDDI to be
> > built-in to build without errors.
> > 
> > Prevents these build errors:
> > s390-linux-ld: drivers/s390/net/lcs.o: in function `lcs_new_device':
> > drivers/s390/net/lcs.c:2150: undefined reference to `fddi_type_trans'
> > s390-linux-ld: drivers/s390/net/lcs.c:2151: undefined reference to `alloc_fddidev'
> > 
> > This FDDI requirement effectively restores the previous condition
> > before the blamed patch, when #ifdef CONFIG_FDDI was used, without
> > testing for CONFIG_FDDI_MODULE.
> > 
> > Fixes: 128272336120 ("s390/net: lcs: use IS_ENABLED() for kconfig detection")
> > Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
> > Reported-by: kernel test robot <lkp@intel.com>
> > Link: lore.kernel.org/r/202306202129.pl0AqK8G-lkp@intel.com
> > Suggested-by: Simon Horman <simon.horman@corigine.com>
> > Cc: Alexandra Winter <wintera@linux.ibm.com>
> > Cc: Wenjia Zhang <wenjia@linux.ibm.com>
> > Cc: linux-s390@vger.kernel.org
> > Cc: netdev@vger.kernel.org
> > Cc: Heiko Carstens <hca@linux.ibm.com>
> > Cc: Vasily Gorbik <gor@linux.ibm.com>
> > Cc: Alexander Gordeev <agordeev@linux.ibm.com>
> > Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
> > Cc: Sven Schnelle <svens@linux.ibm.com>
> > Cc: David S. Miller <davem@davemloft.net>
> > Cc: Eric Dumazet <edumazet@google.com>
> > Cc: Jakub Kicinski <kuba@kernel.org>
> > Cc: Paolo Abeni <pabeni@redhat.com>
> > ---
> >  drivers/s390/net/Kconfig |    2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff -- a/drivers/s390/net/Kconfig b/drivers/s390/net/Kconfig
> > --- a/drivers/s390/net/Kconfig
> > +++ b/drivers/s390/net/Kconfig
> > @@ -6,11 +6,13 @@ config LCS
> >  	def_tristate m
> >  	prompt "Lan Channel Station Interface"
> >  	depends on CCW && NETDEVICES && (ETHERNET || FDDI)
> > +	depends on FDDI=y || FDDI=n
> >  	help
> >  	  Select this option if you want to use LCS networking on IBM System z.
> >  	  This device driver supports FDDI (IEEE 802.7) and Ethernet.
> >  	  To compile as a module, choose M. The module name is lcs.
> >  	  If you do not know what it is, it's safe to choose Y.
> > +	  If FDDI is used, it must be built-in (=y).
> >  
> >  config CTCM
> >  	def_tristate m
> > 
> 
> 
> Wow Randy and Simon, you are reacting faster than I was able to evaluate this yesterday.
> 2 thoughts:
> 
> 1) As ETHERNET cannot be a module and this patch prevents FDDI from being a module, then 
> 128272336120 ("s390/net: lcs: use IS_ENABLED() for kconfig detection")
> is kind of pointless and can as well be reverted instead of doing this fix.
> Or am I missing something?

I'll leave that one to Randy at this point.

> 2) I wonder whether
> 
>   	depends on CCW && NETDEVICES && (ETHERNET || FDDI)
>  +	depends on FDDI || FDDI=n
> 
> would do what we want here:
> When FDDI is a loadable module, LCS mustn't be built-in.
> 
> I will do some experiments and let you know.

It does seem to on my side.
But checking would be much appreciated.