[PATCH v9 31/38] phy: core: add notifier infrastructure

[Sebastian Reichel <sebastian.reichel@collabora.com>]

Some PHY devices with multiple ports (e.g. USB3 and DP) require a reset
if the configuration changes or cable orientation changes. This is a
problem, as the consumer device will run into undefined behavior.

With the new PHY notifier API introduced in this patch, the consumer
driver can hook into reset events coming from a PHY device to handle the
PHY going down gracefully.

Note that this uses -ENOSYS instead of the more sensible -ENOTSUP for
the stub functions when GENERIC_PHY is disabled to stay consistent with
the existing ones.

Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
---
 drivers/phy/phy-core.c  | 57 +++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/phy/phy.h | 40 ++++++++++++++++++++++++++++++++++
 2 files changed, 97 insertions(+)

diff --git a/drivers/phy/phy-core.c b/drivers/phy/phy-core.c
index 21aaf2f76e53..533473d975d3 100644
--- a/drivers/phy/phy-core.c
+++ b/drivers/phy/phy-core.c
@@ -542,6 +542,62 @@ int phy_notify_state(struct phy *phy, union phy_notify state)
 }
 EXPORT_SYMBOL_GPL(phy_notify_state);
 
+/**
+ * phy_register_notifier() - register a notifier for PHY events
+ * @phy: the phy returned by phy_get()
+ * @nb: notifier block to register
+ *
+ * Allows PHY consumers to receive notifications about PHY reset events.
+ * PHY providers can signal these events using phy_notify_reset().
+ *
+ * Returns: %0 if successful, a negative error code otherwise
+ */
+int phy_register_notifier(struct phy *phy, struct notifier_block *nb)
+{
+	if (!phy)
+		return 0;
+
+	return blocking_notifier_chain_register(&phy->notifier, nb);
+}
+EXPORT_SYMBOL_GPL(phy_register_notifier);
+
+/**
+ * phy_unregister_notifier() - unregister a notifier for PHY events
+ * @phy: the phy returned by phy_get()
+ * @nb: notifier block to unregister
+ *
+ * Returns: %0 if successful, a negative error code otherwise
+ */
+int phy_unregister_notifier(struct phy *phy, struct notifier_block *nb)
+{
+	if (!phy)
+		return 0;
+
+	return blocking_notifier_chain_unregister(&phy->notifier, nb);
+}
+EXPORT_SYMBOL_GPL(phy_unregister_notifier);
+
+/**
+ * phy_notify_reset() - notify consumers of a PHY reset event
+ * @phy: the phy that is being reset
+ * @event: the notification event (PRE_RESET or POST_RESET)
+ *
+ * Called by PHY providers to notify consumers that the PHY is about to
+ * be reset or has completed a reset. This allows consumers to quiesce
+ * hardware before the PHY becomes unavailable.
+ *
+ * Returns: %0 if successful or no notifiers registered, a negative error
+ * code if a notifier returns an error (for PRE_RESET only)
+ */
+int phy_notify_reset(struct phy *phy, enum phy_notification event)
+{
+	if (!phy)
+		return 0;
+
+	return blocking_notifier_call_chain(&phy->notifier, event, phy);
+}
+EXPORT_SYMBOL_GPL(phy_notify_reset);
+
 /**
  * phy_configure() - Changes the phy parameters
  * @phy: the phy returned by phy_get()
@@ -1018,6 +1074,7 @@ struct phy *phy_create(struct device *dev, struct device_node *node,
 	device_initialize(&phy->dev);
 	lockdep_register_key(&phy->lockdep_key);
 	mutex_init_with_key(&phy->mutex, &phy->lockdep_key);
+	BLOCKING_INIT_NOTIFIER_HEAD(&phy->notifier);
 
 	phy->dev.class = &phy_class;
 	phy->dev.parent = dev;
diff --git a/include/linux/phy/phy.h b/include/linux/phy/phy.h
index ea47975e288a..3779a4d0a02c 100644
--- a/include/linux/phy/phy.h
+++ b/include/linux/phy/phy.h
@@ -11,6 +11,7 @@
 #define __DRIVERS_PHY_H
 
 #include <linux/err.h>
+#include <linux/notifier.h>
 #include <linux/of.h>
 #include <linux/device.h>
 #include <linux/pm_runtime.h>
@@ -53,6 +54,16 @@ enum phy_media {
 	PHY_MEDIA_DAC,
 };
 
+/**
+ * enum phy_notification - PHY notification events
+ * @PHY_NOTIFY_PRE_RESET: PHY is about to be reset, consumers should quiesce
+ * @PHY_NOTIFY_POST_RESET: PHY reset is complete, consumers may resume
+ */
+enum phy_notification {
+	PHY_NOTIFY_PRE_RESET,
+	PHY_NOTIFY_POST_RESET,
+};
+
 enum phy_ufs_state {
 	PHY_UFS_HIBERN8_ENTER,
 	PHY_UFS_HIBERN8_EXIT,
@@ -170,6 +181,7 @@ struct phy_attrs {
  * @power_count: used to protect when the PHY is used by multiple consumers
  * @attrs: used to specify PHY specific attributes
  * @pwr: power regulator associated with the phy
+ * @notifier: notifier head for PHY reset events
  * @debugfs: debugfs directory
  */
 struct phy {
@@ -182,6 +194,7 @@ struct phy {
 	int			power_count;
 	struct phy_attrs	attrs;
 	struct regulator	*pwr;
+	struct blocking_notifier_head notifier;
 	struct dentry		*debugfs;
 };
 
@@ -267,6 +280,9 @@ int phy_calibrate(struct phy *phy);
 int phy_notify_connect(struct phy *phy, int port);
 int phy_notify_disconnect(struct phy *phy, int port);
 int phy_notify_state(struct phy *phy, union phy_notify state);
+int phy_register_notifier(struct phy *phy, struct notifier_block *nb);
+int phy_unregister_notifier(struct phy *phy, struct notifier_block *nb);
+int phy_notify_reset(struct phy *phy, enum phy_notification event);
 static inline int phy_get_bus_width(struct phy *phy)
 {
 	return phy->attrs.bus_width;
@@ -428,6 +444,30 @@ static inline int phy_notify_state(struct phy *phy, union phy_notify state)
 	return -ENOSYS;
 }
 
+static inline int phy_register_notifier(struct phy *phy,
+					struct notifier_block *nb)
+{
+	if (!phy)
+		return 0;
+	return -ENOSYS;
+}
+
+static inline int phy_unregister_notifier(struct phy *phy,
+					  struct notifier_block *nb)
+{
+	if (!phy)
+		return 0;
+	return -ENOSYS;
+}
+
+static inline int phy_notify_reset(struct phy *phy,
+				   enum phy_notification event)
+{
+	if (!phy)
+		return 0;
+	return -ENOSYS;
+}
+
 static inline int phy_configure(struct phy *phy,
 				union phy_configure_opts *opts)
 {

-- 
2.53.0