[PATCH v11 15/25] firmware: arm_scmi: Add common per-protocol debugfs support

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

Allow interested SCMI protocols to register their own specific debugfs
entries under a common per-instance and per-protocol subtree rooted
at /sys/kernel/debug/scmi/<N>/protocols/<PROTO_ID>/

Expose a helper to enable protocol initialization code to get access to
such per-protocol/per-instance dentries in order to be able to install
their own dedicated debugfs entries.

Per-protocol debugfs support is configurable and default off.

Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
---
v8 --> v9
 - avoid NULL deref on DBG cleanup path
v5 --> v6
 - bail out of dentry_get helper when SCMI debug susbsytem failed to init
 - remove stale SCMI protocol operations
 - add a preoper clean up of debugfs when protocol init fails
---
 drivers/firmware/arm_scmi/Kconfig     | 14 +++++++++++
 drivers/firmware/arm_scmi/common.h    |  2 ++
 drivers/firmware/arm_scmi/driver.c    | 35 +++++++++++++++++++++++++--
 drivers/firmware/arm_scmi/protocols.h |  6 +++++
 include/linux/scmi_protocol.h         |  1 -
 5 files changed, 55 insertions(+), 3 deletions(-)

diff --git a/drivers/firmware/arm_scmi/Kconfig b/drivers/firmware/arm_scmi/Kconfig
index 783c24a20e29..f506c4d1d96a 100644
--- a/drivers/firmware/arm_scmi/Kconfig
+++ b/drivers/firmware/arm_scmi/Kconfig
@@ -69,6 +69,20 @@ config ARM_SCMI_DEBUG_COUNTERS
 	  such useful debug counters. This can be helpful for debugging and
 	  SCMI monitoring.
 
+config ARM_SCMI_DEBUG_PROTOCOLS
+	bool "Enable SCMI protocols debug"
+	select ARM_SCMI_NEED_DEBUGFS
+	depends on DEBUG_FS
+	default n
+	help
+	  Enables per-protocol specific debug features, where available.
+	  When provided, such per-protocol debugfs entries are grouped
+	  inside a common a subtree named by the protocol number and rooted
+	  under a per-instance 'protocols' directory.
+
+	  Such per-protocol entries subtree structure is freely defined
+	  within the related protocol code.
+
 config ARM_SCMI_QUIRKS
 	bool "Enable SCMI Quirks framework"
 	depends on JUMP_LABEL || COMPILE_TEST
diff --git a/drivers/firmware/arm_scmi/common.h b/drivers/firmware/arm_scmi/common.h
index 1d9e6af09672..8c0e49748c32 100644
--- a/drivers/firmware/arm_scmi/common.h
+++ b/drivers/firmware/arm_scmi/common.h
@@ -324,6 +324,7 @@ enum debug_counters {
 /**
  * struct scmi_debug_info  - Debug common info
  * @top_dentry: A reference to the top debugfs dentry
+ * @protos: A reference to the top debugfs protocols subdirectory
  * @name: Name of this SCMI instance
  * @type: Type of this SCMI instance
  * @is_atomic: Flag to state if the transport of this instance is atomic
@@ -331,6 +332,7 @@ enum debug_counters {
  */
 struct scmi_debug_info {
 	struct dentry *top_dentry;
+	struct dentry *protos;
 	const char *name;
 	const char *type;
 	bool is_atomic;
diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
index 408fa4cb83a6..e8d93690ecc2 100644
--- a/drivers/firmware/arm_scmi/driver.c
+++ b/drivers/firmware/arm_scmi/driver.c
@@ -18,6 +18,7 @@
 
 #include <linux/bitmap.h>
 #include <linux/cleanup.h>
+#include <linux/dcache.h>
 #include <linux/debugfs.h>
 #include <linux/device.h>
 #include <linux/export.h>
@@ -102,6 +103,8 @@ struct scmi_xfers_info {
  *			has completed.
  * @ph: An embedded protocol handle that will be passed down to protocol
  *	initialization code to identify this instance.
+ * @dbg: An optional reference to this protocol top debugfs directory; it will
+ *	 be automatically recursively removed on protocol de-initialization.
  *
  * Each protocol is initialized independently once for each SCMI platform in
  * which is defined by DT and implemented by the SCMI server fw.
@@ -116,6 +119,7 @@ struct scmi_protocol_instance {
 	unsigned int			version;
 	unsigned int			negotiated_version;
 	struct scmi_protocol_handle	ph;
+	struct dentry			*dbg;
 };
 
 #define ph_to_pi(h)	container_of(h, struct scmi_protocol_instance, ph)
@@ -2094,6 +2098,25 @@ static void scmi_common_fastchannel_db_ring(struct scmi_fc_db_info *db)
 		SCMI_PROTO_FC_RING_DB(64);
 }
 
+static struct dentry *
+scmi_debugfs_proto_dentry_get(const struct scmi_protocol_handle *ph)
+{
+	struct scmi_protocol_instance *pi = ph_to_pi(ph);
+	struct scmi_info *info = handle_to_scmi_info(pi->handle);
+
+	if (!IS_ENABLED(CONFIG_ARM_SCMI_DEBUG_PROTOCOLS) || !info->dbg)
+		return ERR_PTR(-ENODEV);
+
+	if (!pi->dbg) {
+		char proto_dir[8];
+
+		snprintf(proto_dir, 8, "0x%02X", pi->proto->id);
+		pi->dbg = debugfs_create_dir(proto_dir, info->dbg->protos);
+	}
+
+	return pi->dbg;
+}
+
 static const struct scmi_proto_helpers_ops helpers_ops = {
 	.extended_name_get = scmi_common_extended_name_get,
 	.get_max_msg_size = scmi_common_get_max_msg_size,
@@ -2104,6 +2127,7 @@ static const struct scmi_proto_helpers_ops helpers_ops = {
 	.protocol_msg_check = scmi_protocol_msg_check,
 	.fastchannel_init = scmi_common_fastchannel_init,
 	.fastchannel_db_ring = scmi_common_fastchannel_db_ring,
+	.debugfs_proto_dentry_get = scmi_debugfs_proto_dentry_get,
 };
 
 /**
@@ -2289,12 +2313,12 @@ scmi_alloc_init_protocol_instance(struct scmi_info *info,
 	/* proto->init is assured NON NULL by scmi_protocol_register */
 	ret = pi->proto->instance_init(&pi->ph);
 	if (ret)
-		goto clean;
+		goto clean_dbg;
 
 	ret = idr_alloc(&info->protocols, pi, proto->id, proto->id + 1,
 			GFP_KERNEL);
 	if (ret != proto->id)
-		goto clean;
+		goto clean_dbg;
 
 	/*
 	 * Warn but ignore events registration errors since we do not want
@@ -2315,6 +2339,8 @@ scmi_alloc_init_protocol_instance(struct scmi_info *info,
 
 	return pi;
 
+clean_dbg:
+	debugfs_remove_recursive(pi->dbg);
 clean:
 	/* Take care to put the protocol module's owner before releasing all */
 	scmi_protocol_put(proto);
@@ -2430,6 +2456,8 @@ void scmi_protocol_release(const struct scmi_handle *handle, u8 protocol_id)
 	if (refcount_dec_and_test(&pi->users)) {
 		void *gid = pi->gid;
 
+		debugfs_remove_recursive(pi->dbg);
+
 		if (pi->proto->events)
 			scmi_deregister_protocol_events(handle, protocol_id);
 
@@ -3169,6 +3197,9 @@ static struct scmi_debug_info *scmi_debugfs_common_setup(struct scmi_info *info)
 	if (IS_ENABLED(CONFIG_ARM_SCMI_DEBUG_COUNTERS))
 		scmi_debugfs_counters_setup(dbg, trans);
 
+	if (IS_ENABLED(CONFIG_ARM_SCMI_DEBUG_PROTOCOLS))
+		dbg->protos = debugfs_create_dir("protocols", top_dentry);
+
 	dbg->top_dentry = top_dentry;
 
 	if (devm_add_action_or_reset(info->dev,
diff --git a/drivers/firmware/arm_scmi/protocols.h b/drivers/firmware/arm_scmi/protocols.h
index 1f9925b8f495..04e196a9fbf4 100644
--- a/drivers/firmware/arm_scmi/protocols.h
+++ b/drivers/firmware/arm_scmi/protocols.h
@@ -11,6 +11,7 @@
 
 #include <linux/bitfield.h>
 #include <linux/completion.h>
+#include <linux/debugfs.h>
 #include <linux/device.h>
 #include <linux/errno.h>
 #include <linux/kernel.h>
@@ -284,6 +285,9 @@ struct scmi_fc_info {
  *		      gathering FC descriptions from the SCMI platform server.
  * @fastchannel_db_ring: A common helper to ring a FC doorbell.
  * @get_max_msg_size: A common helper to get the maximum message size.
+ * @debugfs_proto_dentry_get: A common helper to get a per-protocol debugfs top
+ *			      directory to use as a root. It will be
+ *			      recursively removed on protocol de-initialization.
  */
 struct scmi_proto_helpers_ops {
 	int (*extended_name_get)(const struct scmi_protocol_handle *ph,
@@ -307,6 +311,8 @@ struct scmi_proto_helpers_ops {
 				 u32 *rate_limit);
 	void (*fastchannel_db_ring)(struct scmi_fc_db_info *db);
 	int (*get_max_msg_size)(const struct scmi_protocol_handle *ph);
+	struct dentry *(*debugfs_proto_dentry_get)
+		(const struct scmi_protocol_handle *ph);
 };
 
 /**
diff --git a/include/linux/scmi_protocol.h b/include/linux/scmi_protocol.h
index 83ab8edc0b13..037b486dc873 100644
--- a/include/linux/scmi_protocol.h
+++ b/include/linux/scmi_protocol.h
@@ -1156,7 +1156,6 @@ struct scmi_handle {
 	void (*devm_protocol_put)(struct scmi_device *sdev, u8 proto);
 	bool (*is_transport_atomic)(const struct scmi_handle *handle,
 				    unsigned int *atomic_threshold);
-
 	const struct scmi_notify_ops *notify_ops;
 };
 
-- 
2.54.0