linux-kernel - Re: [PATCH 2/3] net: dsa: tag_ocelot

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Date:   Thu, 25 Feb 2021 15:47:41 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Networking <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] net: dsa: tag_ocelot_8021q: fix driver dependency

On Thu, Feb 25, 2021 at 3:43 PM Vladimir Oltean <olteanv@...il.com> wrote:
>
> On Thu, Feb 25, 2021 at 03:38:32PM +0100, Arnd Bergmann wrote:
> > From: Arnd Bergmann <arnd@...db.de>
> >
> > When the ocelot driver code is in a library, the dsa tag
> > code cannot be built-in:
> >
> > ld.lld: error: undefined symbol: ocelot_can_inject
> > >>> referenced by tag_ocelot_8021q.c
> > >>>               dsa/tag_ocelot_8021q.o:(ocelot_xmit) in archive net/built-in.a
> >
> > ld.lld: error: undefined symbol: ocelot_port_inject_frame
> > >>> referenced by tag_ocelot_8021q.c
> > >>>               dsa/tag_ocelot_8021q.o:(ocelot_xmit) in archive net/built-in.a
> >
> > Building the tag support only really makes sense for compile-testing
> > when the driver is available, so add a Kconfig dependency that prevents
> > the broken configuration while allowing COMPILE_TEST alternative when
> > MSCC_OCELOT_SWITCH_LIB is disabled entirely.  This case is handled
> > through the #ifdef check in include/soc/mscc/ocelot.h.
> >
> > Fixes: 0a6f17c6ae21 ("net: dsa: tag_ocelot_8021q: add support for PTP timestamping")
> > Signed-off-by: Arnd Bergmann <arnd@...db.de>
> > ---
> >  net/dsa/Kconfig | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/net/dsa/Kconfig b/net/dsa/Kconfig
> > index 3589224c8da9..58b8fc82cd3c 100644
> > --- a/net/dsa/Kconfig
> > +++ b/net/dsa/Kconfig
> > @@ -118,6 +118,8 @@ config NET_DSA_TAG_OCELOT
> >
> >  config NET_DSA_TAG_OCELOT_8021Q
> >       tristate "Tag driver for Ocelot family of switches, using VLAN"
> > +     depends on MSCC_OCELOT_SWITCH_LIB || \
> > +               (MSCC_OCELOT_SWITCH_LIB=n && COMPILE_TEST)
> >       select NET_DSA_TAG_8021Q
> >       help
> >         Say Y or M if you want to enable support for tagging frames with a
> > --
> > 2.29.2
> >
>
> Why isn't this code in include/soc/mscc/ocelot.h enough?
>
> #if IS_ENABLED(CONFIG_MSCC_OCELOT_SWITCH_LIB)
>
> bool ocelot_can_inject(struct ocelot *ocelot, int grp);
> void ocelot_port_inject_frame(struct ocelot *ocelot, int port, int grp,
>                               u32 rew_op, struct sk_buff *skb);
> int ocelot_xtr_poll_frame(struct ocelot *ocelot, int grp, struct sk_buff **skb);
> void ocelot_drain_cpu_queue(struct ocelot *ocelot, int grp);
>
> #else
>
> static inline bool ocelot_can_inject(struct ocelot *ocelot, int grp)
> {
>         return false;
> }

That code is in include/soc/mscc/ocelot.h, it is what causes the
problem with CONFIG_MSCC_OCELOT_SWITCH_LIB=m
and NET_DSA_TAG_OCELOT_8021Q=y, as I tried to explain.

         Arnd