firmware: arm_scmi: Add optional transport_init/exit support

Some SCMI transport could need to perform some transport specific setup
before they can be used by the SCMI core transport layer: typically this
early setup consists in registering with some other kernel subsystem.

Add the optional capability for a transport to provide a couple of init
and exit functions that are assured to be called early during the SCMI
core initialization phase, well before the SCMI core probing step.

[ Peter: Adapted RFC patch by Cristian for submission to upstream. ]

Link: https://lore.kernel.org/r/20210803131024.40280-4-cristian.marussi@arm.comSigned-off-by: NPeter Hilber <peter.hilber@opensynergy.com>
[ Cristian: Fixed scmi_transports_exit point of invocation ]
Signed-off-by: NCristian Marussi <cristian.marussi@arm.com>
Signed-off-by: NSudeep Holla <sudeep.holla@arm.com>

drivers/firmware/arm_scmi/common.h

@@ -321,6 +321,12 @@ struct scmi_device *scmi_child_dev_find(struct device *parent,
 /**
  * struct scmi_desc - Description of SoC integration
  *
+ * @transport_init: An optional function that a transport can provide to
+ *		    initialize some transport-specific setup during SCMI core
+ *		    initialization, so ahead of SCMI core probing.
+ * @transport_exit: An optional function that a transport can provide to
+ *		    de-initialize some transport-specific setup during SCMI core
+ *		    de-initialization, so after SCMI core removal.
  * @ops: Pointer to the transport specific ops structure
  * @max_rx_timeout_ms: Timeout for communication with SoC (in Milliseconds)
  * @max_msg: Maximum number of messages that can be pending
@@ -328,6 +334,8 @@ struct scmi_device *scmi_child_dev_find(struct device *parent,
  * @max_msg_size: Maximum size of data per message that can be handled.
  */
 struct scmi_desc {
+	int (*transport_init)(void);
+	void (*transport_exit)(void);
 	const struct scmi_transport_ops *ops;
 	int max_rx_timeout_ms;
 	int max_msg;

drivers/firmware/arm_scmi/driver.c

@@ -1581,10 +1581,65 @@ static struct platform_driver scmi_driver = {
 	.remove = scmi_remove,
 };
 
+/**
+ * __scmi_transports_setup  - Common helper to call transport-specific
+ * .init/.exit code if provided.
+ *
+ * @init: A flag to distinguish between init and exit.
+ *
+ * Note that, if provided, we invoke .init/.exit functions for all the
+ * transports currently compiled in.
+ *
+ * Return: 0 on Success.
+ */
+static inline int __scmi_transports_setup(bool init)
+{
+	int ret = 0;
+	const struct of_device_id *trans;
+
+	for (trans = scmi_of_match; trans->data; trans++) {
+		const struct scmi_desc *tdesc = trans->data;
+
+		if ((init && !tdesc->transport_init) ||
+		    (!init && !tdesc->transport_exit))
+			continue;
+
+		if (init)
+			ret = tdesc->transport_init();
+		else
+			tdesc->transport_exit();
+
+		if (ret) {
+			pr_err("SCMI transport %s FAILED initialization!\n",
+			       trans->compatible);
+			break;
+		}
+	}
+
+	return ret;
+}
+
+static int __init scmi_transports_init(void)
+{
+	return __scmi_transports_setup(true);
+}
+
+static void __exit scmi_transports_exit(void)
+{
+	__scmi_transports_setup(false);
+}
+
 static int __init scmi_driver_init(void)
 {
+	int ret;
+
 	scmi_bus_init();
 
+	/* Initialize any compiled-in transport which provided an init/exit */
+	ret = scmi_transports_init();
+	if (ret)
+		return ret;
+
 	scmi_base_register();
 
 	scmi_clock_register();
@@ -1613,6 +1668,8 @@ static void __exit scmi_driver_exit(void)
 
 	scmi_bus_exit();
 
+	scmi_transports_exit();
+
 	platform_driver_unregister(&scmi_driver);
 }
 module_exit(scmi_driver_exit);