firmware: arm_scmi: Add optional link_supplier() transport op

Some transports are also effectively registered with other kernel subsystem
in order to be properly probed and initialized; as a consequence such kind
of transports, and their related devices, might still not have been probed
and initialized at the time the main SCMI core driver is probed.

Add an optional .link_supplier() transport operation which can be used by
the core SCMI stack to dynamically check if the transport is ready and
dynamically link its device to the SCMI platform instance device.

Link: https://lore.kernel.org/r/20210803131024.40280-13-cristian.marussi@arm.com
Signed-off-by: Peter Hilber <peter.hilber@opensynergy.com>
[ Cristian: reworded commit message ]
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

drivers/firmware/arm_scmi/common.h

@@ -348,6 +348,7 @@ struct scmi_chan_info {
 /**
  * struct scmi_transport_ops - Structure representing a SCMI transport ops
  *
+ * @link_supplier: Optional callback to add link to a supplier device
  * @chan_available: Callback to check if channel is available or not
  * @chan_setup: Callback to allocate and setup a channel
  * @chan_free: Callback to free a channel
@@ -362,6 +363,7 @@ struct scmi_chan_info {
  * @poll_done: Callback to poll transfer status
  */
 struct scmi_transport_ops {
+	int (*link_supplier)(struct device *dev);
 	bool (*chan_available)(struct device *dev, int idx);
 	int (*chan_setup)(struct scmi_chan_info *cinfo, struct device *dev,
 			  bool tx);

drivers/firmware/arm_scmi/driver.c

@@ -1814,6 +1814,12 @@ static int scmi_probe(struct platform_device *pdev)
 	handle->devm_protocol_get = scmi_devm_protocol_get;
 	handle->devm_protocol_put = scmi_devm_protocol_put;
 
+	if (desc->ops->link_supplier) {
+		ret = desc->ops->link_supplier(dev);
+		if (ret)
+			return ret;
+	}
+
 	ret = scmi_txrx_setup(info, dev, SCMI_PROTOCOL_BASE);
 	if (ret)
 		return ret;