[PATCH v7 03/23] firmware: arm_scmi: Introduce protocol instance notifiers

[Cristian Marussi <cristian.marussi@arm.com>]

Allow protocols themselves to register for their own notifications and
provide their own notifier callbacks. Each protocol can now register one
unique per-protocol instance notifier block whose callback will be
registered on the proper notification chain as usual: such notifier will
be automatically removed during the protocol de-initialiazation phase.

Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
---
v5 -->v6
 - move protocol notifier registration out of proto_init
v2-->v3
 - split out unrelated changes on event sizing
v1-->v2
 - Fixed multiline comment format
---
 drivers/firmware/arm_scmi/common.h    | 12 ++++
 drivers/firmware/arm_scmi/driver.c    | 86 +++++++++++++++++++++------
 drivers/firmware/arm_scmi/notify.c    | 14 +++++
 drivers/firmware/arm_scmi/protocols.h | 10 ++++
 4 files changed, 103 insertions(+), 19 deletions(-)

diff --git a/drivers/firmware/arm_scmi/common.h b/drivers/firmware/arm_scmi/common.h
index 767f08be416c..f8fbb1a46482 100644
--- a/drivers/firmware/arm_scmi/common.h
+++ b/drivers/firmware/arm_scmi/common.h
@@ -18,6 +18,7 @@
 #include <linux/list.h>
 #include <linux/module.h>
 #include <linux/property.h>
+#include <linux/notifier.h>
 #include <linux/refcount.h>
 #include <linux/scmi_protocol.h>
 #include <linux/spinlock.h>
@@ -708,8 +709,19 @@ static struct platform_driver __drv = {					       \
 	.probe = __tag##_probe,						       \
 }
 
+struct scmi_protocol_notifier {
+	u8 proto_id;
+	u8 evt_id;
+	const u32 *src_id;
+	struct notifier_block *nb;
+};
+
 void scmi_notification_instance_data_set(const struct scmi_handle *handle,
 					 void *priv);
 void *scmi_notification_instance_data_get(const struct scmi_handle *handle);
+int scmi_protocol_notifier_register(const struct scmi_handle *handle,
+				    struct scmi_protocol_notifier *pno);
+int scmi_protocol_notifier_unregister(const struct scmi_handle *handle,
+				      struct scmi_protocol_notifier *pno);
 int scmi_inflight_count(const struct scmi_handle *handle);
 #endif /* _SCMI_COMMON_H */
diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
index 8e06e40d1a11..0f9e8dfc6137 100644
--- a/drivers/firmware/arm_scmi/driver.c
+++ b/drivers/firmware/arm_scmi/driver.c
@@ -90,6 +90,8 @@ struct scmi_xfers_info {
  * @gid: A reference for per-protocol devres management.
  * @users: A refcount to track effective users of this protocol.
  * @priv: Reference for optional protocol private data.
+ * @pno: A protocol instance notifier descriptor: active only when the
+ *	 included notifier block @nb is non-NULL.
  * @version: Protocol version supported by the platform as detected at runtime.
  * @negotiated_version: When the platform supports a newer protocol version,
  *			the agent will try to negotiate with the platform the
@@ -109,6 +111,7 @@ struct scmi_protocol_instance {
 	void				*gid;
 	refcount_t			users;
 	void				*priv;
+	struct scmi_protocol_notifier   pno;
 	unsigned int			version;
 	unsigned int			negotiated_version;
 	struct scmi_protocol_handle	ph;
@@ -1657,6 +1660,24 @@ static void *scmi_get_protocol_priv(const struct scmi_protocol_handle *ph)
 	return pi->priv;
 }
 
+static int
+scmi_register_instance_notifier(const struct scmi_protocol_handle *ph, u8 evt_id,
+				const u32 *src_id, struct notifier_block *nb)
+{
+	struct scmi_protocol_instance *pi = ph_to_pi(ph);
+
+	pi->pno.proto_id = pi->proto->id;
+	pi->pno.evt_id = evt_id;
+	pi->pno.src_id = src_id;
+	/*
+	 * Ensure the descriptor fields are visibile when the notifier block is
+	 * made available
+	 */
+	smp_store_mb(pi->pno.nb, nb);
+
+	return 0;
+}
+
 static const struct scmi_xfer_ops xfer_ops = {
 	.xfer_get_init = xfer_get_init,
 	.reset_rx_to_maxsz = reset_rx_to_maxsz,
@@ -2257,6 +2278,7 @@ scmi_alloc_init_protocol_instance(struct scmi_info *info,
 	pi->ph.hops = &helpers_ops;
 	pi->ph.set_priv = scmi_set_protocol_priv;
 	pi->ph.get_priv = scmi_get_protocol_priv;
+	pi->ph.instance_notifier_register = scmi_register_instance_notifier;
 	refcount_set(&pi->users, 1);
 
 	/*
@@ -2319,24 +2341,37 @@ static struct scmi_protocol_instance * __must_check
 scmi_get_protocol_instance(const struct scmi_handle *handle, u8 protocol_id)
 {
 	struct scmi_protocol_instance *pi;
+	struct notifier_block *proto_notifier_nb = NULL;
 	struct scmi_info *info = handle_to_scmi_info(handle);
 
-	mutex_lock(&info->protocols_mtx);
-	pi = idr_find(&info->protocols, protocol_id);
+	scoped_guard(mutex, &info->protocols_mtx) {
+		pi = idr_find(&info->protocols, protocol_id);
+		if (pi) {
+			refcount_inc(&pi->users);
+		} else {
+			const struct scmi_protocol *proto;
 
-	if (pi) {
-		refcount_inc(&pi->users);
-	} else {
-		const struct scmi_protocol *proto;
+			/* Fails if protocol not registered on bus */
+			proto = scmi_protocol_get(protocol_id, &info->version);
+			if (!proto)
+				return ERR_PTR(-EPROBE_DEFER);
 
-		/* Fails if protocol not registered on bus */
-		proto = scmi_protocol_get(protocol_id, &info->version);
-		if (proto)
 			pi = scmi_alloc_init_protocol_instance(info, proto);
-		else
-			pi = ERR_PTR(-EPROBE_DEFER);
+			if (IS_ERR(pi))
+				return pi;
+
+			proto_notifier_nb = READ_ONCE(pi->pno.nb);
+		}
+	}
+
+	if (proto_notifier_nb) {
+		int ret;
+
+		ret = scmi_protocol_notifier_register(pi->handle, &pi->pno);
+		if (ret)
+			dev_warn(handle->dev,
+				 "Failed to register protocol notifier\n");
 	}
-	mutex_unlock(&info->protocols_mtx);
 
 	return pi;
 }
@@ -2367,13 +2402,29 @@ int scmi_protocol_acquire(const struct scmi_handle *handle, u8 protocol_id)
 void scmi_protocol_release(const struct scmi_handle *handle, u8 protocol_id)
 {
 	struct scmi_info *info = handle_to_scmi_info(handle);
+	struct notifier_block *proto_notifier_nb = NULL;
 	struct scmi_protocol_instance *pi;
 
-	mutex_lock(&info->protocols_mtx);
-	pi = idr_find(&info->protocols, protocol_id);
-	if (WARN_ON(!pi))
-		goto out;
+	scoped_guard(mutex, &info->protocols_mtx) {
+		pi = idr_find(&info->protocols, protocol_id);
+		if (WARN_ON(!pi))
+			return;
+
+		proto_notifier_nb = pi->pno.nb;
+		/* Ensure NULL is visible */
+		smp_store_mb(pi->pno.nb, NULL);
+	}
 
+	if (proto_notifier_nb) {
+		int ret;
+
+		ret = scmi_protocol_notifier_unregister(pi->handle, &pi->pno);
+		if (ret)
+			dev_err(handle->dev,
+				"Failed to release protocol notifier\n");
+	}
+
+	guard(mutex)(&info->protocols_mtx);
 	if (refcount_dec_and_test(&pi->users)) {
 		void *gid = pi->gid;
 
@@ -2391,9 +2442,6 @@ void scmi_protocol_release(const struct scmi_handle *handle, u8 protocol_id)
 		dev_dbg(handle->dev, "De-Initialized protocol: 0x%X\n",
 			protocol_id);
 	}
-
-out:
-	mutex_unlock(&info->protocols_mtx);
 }
 
 void scmi_setup_protocol_implemented(const struct scmi_protocol_handle *ph,
diff --git a/drivers/firmware/arm_scmi/notify.c b/drivers/firmware/arm_scmi/notify.c
index 8995dd1b12aa..938d575e22fe 100644
--- a/drivers/firmware/arm_scmi/notify.c
+++ b/drivers/firmware/arm_scmi/notify.c
@@ -1420,6 +1420,13 @@ static int scmi_notifier_register(const struct scmi_handle *handle,
 	return ret;
 }
 
+int scmi_protocol_notifier_register(const struct scmi_handle *handle,
+				    struct scmi_protocol_notifier *pno)
+{
+	return scmi_notifier_register(handle, pno->proto_id, pno->evt_id,
+				      pno->src_id, pno->nb);
+}
+
 /**
  * scmi_notifier_unregister()  - Unregister a notifier_block for an event
  * @handle: The handle identifying the platform instance against which the
@@ -1477,6 +1484,13 @@ static int scmi_notifier_unregister(const struct scmi_handle *handle,
 	return 0;
 }
 
+int scmi_protocol_notifier_unregister(const struct scmi_handle *handle,
+				      struct scmi_protocol_notifier *pno)
+{
+	return scmi_notifier_unregister(handle, pno->proto_id, pno->evt_id,
+					pno->src_id, pno->nb);
+}
+
 struct scmi_notifier_devres {
 	const struct scmi_handle *handle;
 	u8 proto_id;
diff --git a/drivers/firmware/arm_scmi/protocols.h b/drivers/firmware/arm_scmi/protocols.h
index 15ad5162e37a..b7f29003a7dc 100644
--- a/drivers/firmware/arm_scmi/protocols.h
+++ b/drivers/firmware/arm_scmi/protocols.h
@@ -166,6 +166,13 @@ struct scmi_proto_helpers_ops;
  *	  can be used by the protocol implementation to generate SCMI messages.
  * @set_priv: A method to set protocol private data for this instance.
  * @get_priv: A method to get protocol private data previously set.
+ * @instance_notifier_register: A method to register interest for specific
+ *				notifications from within a protocol
+ *				implementation unit: ONLY one instance notifier
+ *				can be registered per-protocol.
+ *				The related notifier block will be registered
+ *				right after the protocol is initialized and
+ *				automatically removed on protocol release.
  *
  * This structure represents a protocol initialized against specific SCMI
  * instance and it will be used as follows:
@@ -185,6 +192,9 @@ struct scmi_protocol_handle {
 	const struct scmi_proto_helpers_ops *hops;
 	int (*set_priv)(const struct scmi_protocol_handle *ph, void *priv);
 	void *(*get_priv)(const struct scmi_protocol_handle *ph);
+	int (*instance_notifier_register)(const struct scmi_protocol_handle *ph,
+					  u8 evt_id, const u32 *src_id,
+					  struct notifier_block *nb);
 };
 
 /**
-- 
2.54.0