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

[Jakub Kicinski <kuba@kernel.org>]

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?