Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Tue, 14 Apr 2020 12:23:12 -0300
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     Saeed Mahameed <saeedm@mellanox.com>,
        "narmstrong@baylibre.com" <narmstrong@baylibre.com>,
        "masahiroy@kernel.org" <masahiroy@kernel.org>,
        "Laurent.pinchart@ideasonboard.com" 
        <Laurent.pinchart@ideasonboard.com>,
        "davem@davemloft.net" <davem@davemloft.net>,
        "leon@kernel.org" <leon@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "nico@fluxnic.net" <nico@fluxnic.net>,
        "dri-devel@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>,
        "linux-renesas-soc@vger.kernel.org" 
        <linux-renesas-soc@vger.kernel.org>,
        "kieran.bingham+renesas@ideasonboard.com" 
        <kieran.bingham+renesas@ideasonboard.com>,
        "linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>,
        "jani.nikula@linux.intel.com" <jani.nikula@linux.intel.com>,
        "a.hajda@samsung.com" <a.hajda@samsung.com>,
        "jonas@kwiboo.se" <jonas@kwiboo.se>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "airlied@linux.ie" <airlied@linux.ie>,
        "jernej.skrabec@siol.net" <jernej.skrabec@siol.net>
Subject: Re: [RFC 0/6] Regressions for "imply" behavior change
Message-ID: <20200414152312.GF5100@ziepe.ca>
References: <20200408202711.1198966-1-arnd@arndb.de>
 <nycvar.YSQ.7.76.2004081633260.2671@knanqh.ubzr>
 <CAK8P3a2frDf4BzEpEF0uwPTV2dv6Jve+6N97z1sSuSBUAPJquA@mail.gmail.com>
 <20200408224224.GD11886@ziepe.ca>
 <87k12pgifv.fsf@intel.com>
 <7d9410a4b7d0ef975f7cbd8f0b6762df114df539.camel@mellanox.com>
 <20200410171320.GN11886@ziepe.ca>
 <16441479b793077cdef9658f35773739038c39dc.camel@mellanox.com>
 <20200414132900.GD5100@ziepe.ca>
 <CAK8P3a0aFQ7h4zRDW=QLogXWc88JkJJXEOK0_CpWwsRjq6+T+w@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAK8P3a0aFQ7h4zRDW=QLogXWc88JkJJXEOK0_CpWwsRjq6+T+w@mail.gmail.com>
User-Agent: Mutt/1.9.4 (2018-02-28)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, Apr 14, 2020 at 04:27:41PM +0200, Arnd Bergmann wrote:
> On Tue, Apr 14, 2020 at 3:29 PM Jason Gunthorpe <jgg@ziepe.ca> wrote:
> > On Fri, Apr 10, 2020 at 07:04:27PM +0000, Saeed Mahameed wrote:
> > > On Fri, 2020-04-10 at 14:13 -0300, Jason Gunthorpe wrote:
> > > > On Fri, Apr 10, 2020 at 02:40:42AM +0000, Saeed Mahameed wrote:
> > > >
> > > > > This assumes that the module using FOO has its own flag
> > > > > representing
> > > > > FOO which is not always the case.
> > > > >
> > > > > for example in mlx5 we use VXLAN config flag directly to compile
> > > > > VXLAN related files:
> > > > >
> > > > > mlx5/core/Makefile:
> > > > >
> > > > > obj-$(CONFIG_MLX5_CORE) += mlx5_core.o
> > > > >
> > > > > mlx5_core-y := mlx5_core.o
> > > > > mlx5_core-$(VXLAN) += mlx5_vxlan.o
> > > > >
> > > > > and in mlx5_main.o we do:
> > > >
> > > > Does this work if VXLAN = m ?
> > >
> > > Yes, if VXLAN IS_REACHABLE to MLX5, mlx5_vxlan.o will be
> > > compiled/linked.
> >
> > So mlx5_core-m does the right thing somehow?
> 
> What happens with CONFIG_VXLAN=m is that the above turns into
> 
> mlx5_core-y := mlx5_core.o
> mlx5_core-m += mlx5_vxlan.o
> 
> which in turn leads to mlx5_core.ko *not* containing mlx5_vxlan.o,
> and in turn causing that link error against
> mlx5_vxlan_create/mlx5_vxlan_destroy, unless the IS_ENABLED()
> is changed to IS_REACHABLE().

What about the reverse if mlx5_core is 'm' and VLXAN is 'y'?

 mlx5_core-m := mlx5_core.o
 mlx5_core-y += mlx5_vxlan.o

Magically works out?

> > IIRC that isn't what the expression does, if vxlan is 'n' then
> >   n || !n == true
> 
> It forces MLX5_CORE to 'm' or 'n' but not 'y' if VXLAN=m,
> but allows any option if VXLAN=y

And any option if VXLAN=n ?

Jason