Re: [PATCH net-next] dsa: sja1105: fix reverse dependency

[Vladimir Oltean]

Hi Arnd,

On Thu, Aug 05, 2021 at 01:00:28PM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
>
> The DSA driver and the tag driver for sja1105 are closely linked,
> and recently the dependency started becoming visible in the form
> of the sja1110_process_meta_tstamp() that gets exported by one
> and used by the other.
>
> This causes a rare build failure with CONFIG_NET_DSA_TAG_SJA1105=y
> and CONFIG_NET_DSA_SJA1105=m, as the 'select' statement only
> prevents the opposite configuration:
>
> aarch64-linux-ld: net/dsa/tag_sja1105.o: in function `sja1110_rcv':
> tag_sja1105.c:(.text.sja1110_rcv+0x164): undefined reference to `sja1110_process_meta_tstamp'
>
> Add a stricter dependency for the CONFIG_NET_DSA_TAG_SJA110y to
> prevent it from being built-in when the other one is not.
>
> Fixes: 566b18c8b752 ("net: dsa: sja1105: implement TX timestamping for SJA1110")
> Fixes: 227d07a07ef1 ("net: dsa: sja1105: Add support for traffic through standalone ports")

The second Fixes: tag makes no sense.

> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
> Not sure if there is a more logical way to deal with this,
> but the added dependency does help avoid the build failure.
>
> I found this one while verifying the PTP dependency patch, but
> it's really a separate issue.
> ---
>  net/dsa/Kconfig | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/net/dsa/Kconfig b/net/dsa/Kconfig
> index bca1b5d66df2..548285539752 100644
> --- a/net/dsa/Kconfig
> +++ b/net/dsa/Kconfig
> @@ -138,6 +138,7 @@ config NET_DSA_TAG_LAN9303
>
>  config NET_DSA_TAG_SJA1105
>  	tristate "Tag driver for NXP SJA1105 switches"
> +	depends on NET_DSA_SJA1105 || !NET_DSA_SJA1105

I think I would prefer an optional "build as module if NET_DSA_SJA1105 is a module"
dependency only if NET_DSA_SJA1105_PTP is enabled. I think this is how that is
expressed:

	depends on (NET_DSA_SJA1105 && NET_DSA_SJA1105_PTP) || !NET_DSA_SJA1105 || !NET_DSA_SJA1105_PTP

>  	select PACKING
>  	help
>  	  Say Y or M if you want to enable support for tagging frames with the
> --
> 2.29.2
>