net: Expose available time stamping layers to user space.

Time stamping on network packets may happen either in the MAC or in
the PHY, but not both.  In preparation for making the choice
selectable, expose both the current and available layers via sysfs.

In accordance with the kernel implementation as it stands, the current
layer will always read as "phy" when a PHY time stamping device is
present.  Future patches will allow changing the current layer
administratively.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>

Documentation/ABI/testing/sysfs-class-net-timestamping

@@ -0,0 +1,17 @@
+What:		/sys/class/net/<iface>/available_timestamping_providers
+Date:		January 2022
+Contact:	Richard Cochran <richardcochran@gmail.com>
+Description:
+		Enumerates the available providers for SO_TIMESTAMPING.
+		The possible values are:
+		- "mac"  The MAC provides time stamping.
+		- "phy"  The PHY or MII device provides time stamping.
+
+What:		/sys/class/net/<iface>/current_timestamping_provider
+Date:		January 2022
+Contact:	Richard Cochran <richardcochran@gmail.com>
+Description:
+		Show the current SO_TIMESTAMPING provider.
+		The possible values are:
+		- "mac"  The MAC provides time stamping.
+		- "phy"  The PHY or MII device provides time stamping.

drivers/net/phy/phy_device.c

@@ -1415,6 +1415,7 @@ int phy_attach_direct(struct net_device *dev, struct phy_device *phydev,
 
 	phydev->phy_link_change = phy_link_change;
 	if (dev) {
+		dev->selected_timestamping_layer = PHY_TIMESTAMPING;
 		phydev->attached_dev = dev;
 		dev->phydev = phydev;
 
@@ -1727,6 +1728,7 @@ void phy_detach(struct phy_device *phydev)
 
 	phy_suspend(phydev);
 	if (dev) {
+		dev->selected_timestamping_layer = MAC_TIMESTAMPING;
 		phydev->attached_dev->phydev = NULL;
 		phydev->attached_dev = NULL;
 	}

include/linux/netdevice.h

@@ -1687,6 +1687,11 @@ enum netdev_ml_priv_type {
 	ML_PRIV_CAN,
 };
 
+enum timestamping_layer {
+	MAC_TIMESTAMPING,
+	PHY_TIMESTAMPING,
+};
+
 /**
  *	struct net_device - The DEVICE structure.
  *
@@ -1927,6 +1932,9 @@ enum netdev_ml_priv_type {
  *
  *	@threaded:	napi threaded mode is enabled
  *
+ *	@selected_timestamping_layer:	Tracks whether the MAC or the PHY
+ *					performs packet time stamping.
+ *
  *	@net_notifier_list:	List of per-net netdev notifier block
  *				that follow this device when it is moved
  *				to another network namespace.
@@ -2263,6 +2271,8 @@ struct net_device {
 	unsigned		wol_enabled:1;
 	unsigned		threaded:1;
 
+	enum timestamping_layer selected_timestamping_layer;
+
 	struct list_head	net_notifier_list;
 
 #if IS_ENABLED(CONFIG_MACSEC)

net/core/net-sysfs.c

@@ -618,6 +618,64 @@ static ssize_t threaded_store(struct device *dev,
 }
 static DEVICE_ATTR_RW(threaded);
 
+static ssize_t available_timestamping_providers_show(struct device *dev,
+						     struct device_attribute *attr,
+						     char *buf)
+{
+	const struct ethtool_ops *ops;
+	struct net_device *netdev;
+	struct phy_device *phydev;
+	int ret = 0;
+
+	netdev = to_net_dev(dev);
+	phydev = netdev->phydev;
+	ops = netdev->ethtool_ops;
+
+	if (!rtnl_trylock())
+		return restart_syscall();
+
+	ret += sprintf(buf, "%s\n", "mac");
+	buf += 4;
+
+	if (phy_has_tsinfo(phydev)) {
+		ret += sprintf(buf, "%s\n", "phy");
+		buf += 4;
+	}
+
+	rtnl_unlock();
+
+	return ret;
+}
+static DEVICE_ATTR_RO(available_timestamping_providers);
+
+static ssize_t current_timestamping_provider_show(struct device *dev,
+						  struct device_attribute *attr,
+						  char *buf)
+{
+	const struct ethtool_ops *ops;
+	struct net_device *netdev;
+	struct phy_device *phydev;
+	int ret;
+
+	netdev = to_net_dev(dev);
+	phydev = netdev->phydev;
+	ops = netdev->ethtool_ops;
+
+	if (!rtnl_trylock())
+		return restart_syscall();
+
+	if (phy_has_tsinfo(phydev)) {
+		ret = sprintf(buf, "%s\n", "phy");
+	} else {
+		ret = sprintf(buf, "%s\n", "mac");
+	}
+
+	rtnl_unlock();
+
+	return ret;
+}
+static DEVICE_ATTR_RO(current_timestamping_provider);
+
 static struct attribute *net_class_attrs[] __ro_after_init = {
 	&dev_attr_netdev_group.attr,
 	&dev_attr_type.attr,
@@ -651,6 +709,8 @@ static struct attribute *net_class_attrs[] __ro_after_init = {
 	&dev_attr_carrier_up_count.attr,
 	&dev_attr_carrier_down_count.attr,
 	&dev_attr_threaded.attr,
+	&dev_attr_available_timestamping_providers.attr,
+	&dev_attr_current_timestamping_provider.attr,
 	NULL,
 };
 ATTRIBUTE_GROUPS(net_class);