Re: [PATCH net-next 1/6] ethtool: Add ability to control transceiver modules' power mode

On Sun,  3 Oct 2021 10:32:14 +0300 Ido Schimmel wrote:

From: Ido Schimmel <idosch@nvidia.com>

Add a pair of new ethtool messages, 'ETHTOOL_MSG_MODULE_SET' and
'ETHTOOL_MSG_MODULE_GET', that can be used to control transceiver
modules parameters and retrieve their status.

Acked-by: Jakub Kicinski <kuba@kernel.org>

Couple of take it or leave it comments again, if you prefer to leave as
is that's fine.

+enum ethtool_module_power_mode_policy {
+	ETHTOOL_MODULE_POWER_MODE_POLICY_HIGH,
+	ETHTOOL_MODULE_POWER_MODE_POLICY_AUTO,
+};

I see you left this starting from 0, and we still need a valid bit,
granted just internal to the core.

Would we not need a driver-facing valid bit later on when we extend 
the module API to control more params?  Can't there be drivers which
implement power but don't support the mode policy?

+static int module_set_power_mode(struct net_device *dev, struct nlattr **tb,
+				 bool *p_mod, struct netlink_ext_ack *extack)
+{
+	struct ethtool_module_power_mode_params power = {};
+	struct ethtool_module_power_mode_params power_new;
+	const struct ethtool_ops *ops = dev->ethtool_ops;
+	int ret;
+
+	if (!tb[ETHTOOL_A_MODULE_POWER_MODE_POLICY])
+		return 0;

Feels a little old school to allow set with no attrs, now that we 
do strict validation on attrs across netlink.  What's the reason?

+	if (!ops->get_module_power_mode || !ops->set_module_power_mode) {
+		NL_SET_ERR_MSG_ATTR(extack,
+				    tb[ETHTOOL_A_MODULE_POWER_MODE_POLICY],
+				    "Setting power mode policy is not supported by this device");
+		return -EOPNOTSUPP;
+	}
+
+	power_new.policy = nla_get_u8(tb[ETHTOOL_A_MODULE_POWER_MODE_POLICY]);
+	ret = ops->get_module_power_mode(dev, &power, extack);
+	if (ret < 0)
+		return ret;
+	*p_mod = power_new.policy != power.policy;
+
+	return ops->set_module_power_mode(dev, &power_new, extack);

Why still call set if *p_mod == false?