Re: [PATCH v8 net-next 11/12] net: phy: provide phylib stubs for hardware timestamping operations

[Vladimir Oltean]

On Mon, Jul 17, 2023 at 06:27:08PM +0300, Vladimir Oltean wrote:
> net/core/dev_ioctl.c (built-in code) will want to call phy_mii_ioctl()
> for hardware timestamping purposes. This is not directly possible,
> because phy_mii_ioctl() is a symbol provided under CONFIG_PHYLIB.
> 
> Do something similar to what was done in DSA in commit 5a17818682cf
> ("net: dsa: replace NETDEV_PRE_CHANGE_HWTSTAMP notifier with a stub"),
> and arrange some indirect calls to phy_mii_ioctl() through a stub
> structure containing function pointers, that's provided by phylib as
> built-in even when CONFIG_PHYLIB=m, and which phy_init() populates at
> runtime (module insertion).
> 
> Note: maybe the ownership of the ethtool_phy_ops singleton is backwards,
> and the methods exposed by that should be later merged into phylib_stubs.
> 
> Signed-off-by: Vladimir Oltean <vladimir.oltean@xxxxxxx>
> ---

I should use "git add" on new files more often...

Annex to this patch:

diff --git a/drivers/net/phy/stubs.c b/drivers/net/phy/stubs.c
new file mode 100644
index 000000000000..06498de2d16a
--- /dev/null
+++ b/drivers/net/phy/stubs.c
@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Stubs for PHY library functionality called by the core network stack.
+ * These are necessary because CONFIG_PHYLIB can be a module, and built-in
+ * code cannot directly call symbols exported by modules.
+ */
+#include <net/dsa_stubs.h>
+
+const struct phylib_stubs *phylib_stubs;
+EXPORT_SYMBOL_GPL(phylib_stubs);
diff --git a/include/linux/phylib_stubs.h b/include/linux/phylib_stubs.h
new file mode 100644
index 000000000000..1279f48c8a70
--- /dev/null
+++ b/include/linux/phylib_stubs.h
@@ -0,0 +1,68 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Stubs for the Network PHY library
+ */
+
+#include <linux/rtnetlink.h>
+
+struct kernel_hwtstamp_config;
+struct netlink_ext_ack;
+struct phy_device;
+
+#if IS_ENABLED(CONFIG_PHYLIB)
+
+extern const struct phylib_stubs *phylib_stubs;
+
+struct phylib_stubs {
+	int (*hwtstamp_get)(struct phy_device *phydev,
+			    struct kernel_hwtstamp_config *config);
+	int (*hwtstamp_set)(struct phy_device *phydev,
+			    struct kernel_hwtstamp_config *config,
+			    struct netlink_ext_ack *extack);
+};
+
+static inline int phy_hwtstamp_get(struct phy_device *phydev,
+				   struct kernel_hwtstamp_config *config)
+{
+	/* phylib_register_stubs() and phylib_unregister_stubs()
+	 * also run under rtnl_lock().
+	 */
+	ASSERT_RTNL();
+
+	if (!phylib_stubs)
+		return -EOPNOTSUPP;
+
+	return phylib_stubs->hwtstamp_get(phydev, config);
+}
+
+static inline int phy_hwtstamp_set(struct phy_device *phydev,
+				   struct kernel_hwtstamp_config *config,
+				   struct netlink_ext_ack *extack)
+{
+	/* phylib_register_stubs() and phylib_unregister_stubs()
+	 * also run under rtnl_lock().
+	 */
+	ASSERT_RTNL();
+
+	if (!phylib_stubs)
+		return -EOPNOTSUPP;
+
+	return phylib_stubs->hwtstamp_set(phydev, config, extack);
+}
+
+#else
+
+static inline int phy_hwtstamp_get(struct phy_device *phydev,
+				   struct kernel_hwtstamp_config *config)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline int phy_hwtstamp_set(struct phy_device *phydev,
+				   struct kernel_hwtstamp_config *config,
+				   struct netlink_ext_ack *extack)
+{
+	return -EOPNOTSUPP;
+}
+
+#endif