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Subject[PATCH v5 1/3] firmware: arm_scmi: support only one single SystemPower device
Date
In order to minimize SCMI platform fw-side complexity, only one 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@arm.com>
---
drivers/firmware/arm_scmi/bus.c | 25 +++++++++++++++++++++++++
1 file changed, 25 insertions(+)

diff --git a/drivers/firmware/arm_scmi/bus.c b/drivers/firmware/arm_scmi/bus.c
index 88149a46e6d9..e8542a7e8862 100644
--- a/drivers/firmware/arm_scmi/bus.c
+++ b/drivers/firmware/arm_scmi/bus.c
@@ -19,6 +19,9 @@ static DEFINE_IDA(scmi_bus_id);
static DEFINE_IDR(scmi_available_protocols);
static DEFINE_SPINLOCK(protocol_lock);

+/* Track globally the creation of SCMI SystemPower related devices */
+static bool scmi_syspower_registered;
+
static const struct scmi_device_id *
scmi_dev_match_id(struct scmi_device *scmi_dev, struct scmi_driver *scmi_drv)
{
@@ -175,6 +178,23 @@ scmi_device_create(struct device_node *np, struct device *parent, int protocol,
int id, retval;
struct scmi_device *scmi_dev;

+ /*
+ * Check if any SCMI SystemPower device was already created.
+ *
+ * Note that, shared global @scmi_syspower_registered is not protected
+ * by a mutex since:
+ * - scmi_device_create() is not concurrently invoked by the SCMI core
+ * - scmi_device_destroy() is effectively called only upon SCMI core
+ * unloading/unbinding, so no race is either possible between create
+ * and destroy.
+ */
+ if (protocol == SCMI_PROTOCOL_SYSTEM && scmi_syspower_registered) {
+ dev_warn(parent,
+ "SCMI SystemPower protocol device must be unique !\n");
+ dump_stack();
+ return NULL;
+ }
+
scmi_dev = kzalloc(sizeof(*scmi_dev), GFP_KERNEL);
if (!scmi_dev)
return NULL;
@@ -204,6 +224,9 @@ scmi_device_create(struct device_node *np, struct device *parent, int protocol,
if (retval)
goto put_dev;

+ if (protocol == SCMI_PROTOCOL_SYSTEM)
+ scmi_syspower_registered = true;
+
return scmi_dev;
put_dev:
kfree_const(scmi_dev->name);
@@ -218,6 +241,8 @@ void scmi_device_destroy(struct scmi_device *scmi_dev)
scmi_handle_put(scmi_dev->handle);
ida_simple_remove(&scmi_bus_id, scmi_dev->id);
device_unregister(&scmi_dev->dev);
+ if (scmi_dev->protocol_id == SCMI_PROTOCOL_SYSTEM)
+ scmi_syspower_registered = false;
}

void scmi_set_handle(struct scmi_device *scmi_dev)
--
2.17.1
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