[PATCH 2/5] firmware: arm_scmi: Support only one single SystemPower device

[Cristian Marussi]

In order to minimize SCMI platform fw-side complexity, only one single SCMI
platform should be in charge of SCMI SystemPower protocol communications
with the OSPM: enforce the existence of one single unique device associated
with SystemPower protocol across any possible number of SCMI platforms, and
warn if a system tries to register different SystemPower devices from
multiple platforms.

Signed-off-by: Cristian Marussi <cristian.marussi at arm.com>
---
 drivers/firmware/arm_scmi/bus.c | 31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/arm_scmi/bus.c b/drivers/firmware/arm_scmi/bus.c
index a7cbf4d09081..476855d3dccb 100644
--- a/drivers/firmware/arm_scmi/bus.c
+++ b/drivers/firmware/arm_scmi/bus.c
@@ -19,6 +19,11 @@ static DEFINE_IDA(scmi_bus_id);
 static DEFINE_IDR(scmi_protocols);
 static DEFINE_SPINLOCK(protocol_lock);
 
+/* Track globally the creation of SCMI SystemPower related devices */
+static bool scmi_syspower_registered;
+/* Protect access to scmi_syspower_registered */
+static DEFINE_MUTEX(scmi_syspower_mtx);
+
 static const struct scmi_device_id *
 scmi_dev_match_id(struct scmi_device *scmi_dev, struct scmi_driver *scmi_drv)
 {
@@ -207,11 +212,31 @@ scmi_device_create(struct device_node *np, struct device *parent, int protocol,
 	scmi_dev->dev.release = scmi_device_release;
 	dev_set_name(&scmi_dev->dev, "scmi_dev.%d", id);
 
+	mutex_lock(&scmi_syspower_mtx);
+	if (protocol == SCMI_PROTOCOL_SYSTEM && scmi_syspower_registered) {
+		dev_warn(parent,
+			 "SCMI SystemPower protocol device must be unique !\n");
+
+		mutex_unlock(&scmi_syspower_mtx);
+		ida_free(&scmi_bus_id, id);
+		kfree_const(scmi_dev->name);
+		kfree(scmi_dev);
+		return NULL;
+	}
+
 	retval = device_register(&scmi_dev->dev);
-	if (retval)
+	if (retval) {
+		mutex_unlock(&scmi_syspower_mtx);
 		goto put_dev;
+	}
+
+	if (protocol == SCMI_PROTOCOL_SYSTEM)
+		scmi_syspower_registered = true;
+
+	mutex_unlock(&scmi_syspower_mtx);
 
 	return scmi_dev;
+
 put_dev:
 	kfree_const(scmi_dev->name);
 	put_device(&scmi_dev->dev);
@@ -221,6 +246,10 @@ scmi_device_create(struct device_node *np, struct device *parent, int protocol,
 
 void scmi_device_destroy(struct scmi_device *scmi_dev)
 {
+	mutex_lock(&scmi_syspower_mtx);
+	if (scmi_dev->protocol_id == SCMI_PROTOCOL_SYSTEM)
+		scmi_syspower_registered = false;
+	mutex_unlock(&scmi_syspower_mtx);
 	kfree_const(scmi_dev->name);
 	scmi_handle_put(scmi_dev->handle);
 	ida_free(&scmi_bus_id, scmi_dev->id);
-- 
2.32.0