> I'd suggest
 > 
 >   config IF_IPV6
 > 	bool
 > 	depends on INET
 > 	depends on !(INFINIBAND = y && IPV6 = m)
 > 	default y

Makes sense, will do.  How about calling it INFINIBAND_USE_IPV6 or
something like that, though?  (Since it's under the INFINIBAND config
stuff and exists to forbid INFINIBAND=y && IPV6=m trying to use IPv6).
But see below:

 > but also use it in the source code as a more readable version:
 > 
 > > diff --git a/drivers/infiniband/core/addr.c b/drivers/infiniband/core/addr.c
 > > index d98b05b..ec7abb5 100644
 > > --- a/drivers/infiniband/core/addr.c> +++ b/drivers/infiniband/core/addr.c
 > > @@ -128,6 +128,7 @@ int rdma_translate_ip(struct sockaddr *addr, struct rdma_dev_addr *dev_addr)
 > >  		ret = rdma_copy_addr(dev_addr, dev, NULL);
 > >  		dev_put(dev);
 > >  		break;
 > > +#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
 > 
 > ie use
 > 
 > 	#ifdef CONFIG_IF_IPV6

this doesn't make sense, does it?  Your CONFIG_IF_IPV6 will be set in
the case IPV6=n too I think.  (Which is the whole point... we want to
build this code, just without IPv6 support, if IPv6 is turned off
completely)

 - R.