Re: [PATCH 2/3] net: dsa: tag_ocelot_8021q: fix driver dependency

On Thu, Feb 25, 2021 at 3:43 PM Vladimir Oltean [off-list ref] wrote:

On Thu, Feb 25, 2021 at 03:38:32PM +0100, Arnd Bergmann wrote:

quoted

From: Arnd Bergmann <arnd@arndb.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

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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

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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@arndb.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