Re: [PATCH net-next v9 09/11] onsemi: s2500: Added selftest support to onsemi's S2500 driver

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- [Medium] When CONFIG_NET_SELFTESTS=n, s2500_get_sset_count() returns 0
  for ETH_SS_TEST, because the include/net/selftests.h stub…

--

onsemi: s2500: Added selftest support to onsemi's S2500 driver

This patch adds ethtool selftest support to the onsemi S2500 MAC-PHY
driver. For ETH_SS_TEST it reports the generic net_selftest count and
strings. It also sets net_selftest() as the self_test callback in
s2500_ethtool_ops.

> diff --git a/drivers/net/ethernet/onsemi/s2500/s2500_ethtool.c b/drivers/net/ethernet/onsemi/s2500/s2500_ethtool.c
> index 062cab9460dcf..12e59e8d44a62 100644
> --- a/drivers/net/ethernet/onsemi/s2500/s2500_ethtool.c
> +++ b/drivers/net/ethernet/onsemi/s2500/s2500_ethtool.c

[ ... ]

> @@ -201,6 +202,8 @@ static int s2500_get_sset_count(struct net_device *ndev, int sset)
>  	switch (sset) {
>  	case ETH_SS_STATS:
>  		return S2500_MAC_STATS_LEN;
> +	case ETH_SS_TEST:
> +		return net_selftest_get_count();

[Severity: Medium]
What happens here when CONFIG_NET_SELFTESTS is not enabled?

In that case include/net/selftests.h provides stubs:

static inline int net_selftest_get_count(void)
{
	return 0;
}

So s2500_get_sset_count() returns 0 for ETH_SS_TEST. At the same time,
s2500_ethtool_ops still sets ".self_test = net_selftest", which is the
empty stub.

The ethtool core expects a non-zero count whenever self_test is set. In
net/ethtool/ioctl.c:

ethtool_self_test() {
    ...
	test_len = ops->get_sset_count(dev, ETH_SS_TEST);
	if (test_len < 0)
		return test_len;
	WARN_ON(test_len == 0);
    ...
}

After the warning, the no-op stub runs and "ethtool -t" reports success
without running any tests.

ETHTOOL_GSTRINGS does not require CAP_NET_ADMIN. With
string_set == ETH_SS_TEST, that path also hits a warning:

ethtool_get_strings() {
    ...
	ret = __ethtool_get_sset_count(dev, gstrings.string_set);
	if (ret < 0)
		return ret;
	...
	WARN_ON_ONCE(!ret);
    ...
}

Can this configuration actually be built? NET_SELFTESTS depends on
PHYLIB && INET. S2500_MACPHY only uses imply for it and has no INET
dependency:

config S2500_MACPHY
	tristate "S2500 support"
	depends on SPI
	depends on PTP_1588_CLOCK_OPTIONAL
	imply NET_SELFTESTS

With CONFIG_INET=n, the driver can be built while NET_SELFTESTS=n.

A few existing drivers (fec, ag71xx, asix, lan78xx, smsc95xx) follow
the same pattern.

Would any of these fixes work here?

  - return -EOPNOTSUPP for ETH_SS_TEST when net_selftest_get_count()
    is 0
  - set .self_test only under IS_ENABLED(CONFIG_NET_SELFTESTS)
  - add a dependency on NET_SELFTESTS, and therefore on INET

[ ... ]

-- 
Sashiko AI review · https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20261009-s2500-mac-phy-support-v9-0-dcefe1d0bf0d%40onsemi.com