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

[Vladimir Oltean <olteanv@gmail.com>]

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

static inline void ocelot_port_inject_frame(struct ocelot *ocelot, int port,
					    int grp, u32 rew_op,
					    struct sk_buff *skb)
{
}

static inline int ocelot_xtr_poll_frame(struct ocelot *ocelot, int grp,
					struct sk_buff **skb)
{
	return -EIO;
}

static inline void ocelot_drain_cpu_queue(struct ocelot *ocelot, int grp)
{
}

#endif