[PATCH v2 2/5] software node: add fw_devlink support

[Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>]

Software nodes can be used to describe supplier-consumer relationships
between devices they represent using reference property entries. Unlike
for OF-nodes, driver core cannot yet use these references to create a
probe order that avoids needless probe deferrals on missing providers.

Implement software_node_add_links() modelled on of_fwnode_add_links().
For every DEV_PROP_REF property we resolve each referenced supplier and
create an fwnode link from the node to it. The driver core later promotes
these to device links and defers the consumer until the suppliers are
ready.

There's no allowlist like the one DT needs - devicetree phandles appear
in plenty of non-supplier contexts, but a software node only carries a
reference property when its author explicitly points at another node, so
we treat every reference as an intentional supplier dependency and link
all of them. Graph "remote-endpoint" references are skipped for now: they
go 2-ways between endpoint nodes and would create graph cycles without
the port-parent lifting DT does via get_con_dev(). References to
suppliers that aren't registered yet and self-references are ignored.

fw_devlink resolves the supplier device through fwnode->dev but the core
only records the owning device on the primary fwnode. When the software
node is a device's secondary fwnode, mirror the device pointer onto it in
software_node_notify() so the consumer can actually find the supplier
instead of deferring forever.

While at it: purge the fwnode links in software_node_release() now that
software nodes can own them.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
---
 drivers/base/swnode.c | 79 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)

diff --git a/drivers/base/swnode.c b/drivers/base/swnode.c
index 869228a65cb365567ddac7db6ad7b8743e0dbca9..e6e2d6926fef2db82eb1f2bf439e80aacf48668a 100644
--- a/drivers/base/swnode.c
+++ b/drivers/base/swnode.c
@@ -699,6 +699,62 @@ software_node_graph_parse_endpoint(const struct fwnode_handle *fwnode,
 	return 0;
 }
 
+static int software_node_add_links(struct fwnode_handle *fwnode)
+{
+	const struct software_node_ref_args *ref, *ref_array;
+	struct swnode *swnode = to_swnode(fwnode);
+	const struct property_entry *prop;
+	struct fwnode_handle *refnode;
+	unsigned int count;
+
+	if (!swnode || !swnode->node->properties)
+		return 0;
+
+	/*
+	 * Unlike Device Tree, where phandles appear in many non-supplier
+	 * contexts and a curated allowlist is required, a software node only
+	 * carries a DEV_PROP_REF property when the author explicitly describes
+	 * a reference to another node. Every such reference is therefore an
+	 * intentional supplier dependency, so we create fwnode links for all
+	 * of them.
+	 */
+	for (prop = swnode->node->properties; prop->name; prop++) {
+		if (prop->type != DEV_PROP_REF || prop->is_inline)
+			continue;
+
+		/*
+		 * TODO: Graph "remote-endpoint" references go both ways
+		 * between endpoint child nodes and would create endpoint
+		 * cycles. Let's leave it out for now until we have potential
+		 * users.
+		 */
+		if (!strcmp(prop->name, "remote-endpoint"))
+			continue;
+
+		ref_array = prop->pointer;
+		count = prop->length / sizeof(*ref_array);
+
+		for (unsigned int i = 0; i < count; i++) {
+			ref = &ref_array[i];
+
+			if (ref->swnode)
+				refnode = software_node_fwnode(ref->swnode);
+			else if (ref->fwnode)
+				refnode = ref->fwnode;
+			else
+				continue;
+
+			/* Supplier not registered yet, or self-reference. */
+			if (!refnode || refnode == &swnode->fwnode)
+				continue;
+
+			fwnode_link_add(&swnode->fwnode, refnode, 0);
+		}
+	}
+
+	return 0;
+}
+
 static const struct fwnode_operations software_node_ops = {
 	.get = software_node_get,
 	.put = software_node_put,
@@ -716,6 +772,7 @@ static const struct fwnode_operations software_node_ops = {
 	.graph_get_remote_endpoint = software_node_graph_get_remote_endpoint,
 	.graph_get_port_parent = software_node_graph_get_port_parent,
 	.graph_parse_endpoint = software_node_graph_parse_endpoint,
+	.add_links = software_node_add_links,
 };
 
 /* -------------------------------------------------------------------------- */
@@ -787,6 +844,8 @@ static void software_node_release(struct kobject *kobj)
 {
 	struct swnode *swnode = kobj_to_swnode(kobj);
 
+	fwnode_links_purge(&swnode->fwnode);
+
 	if (swnode->parent) {
 		ida_free(&swnode->parent->child_ids, swnode->id);
 		list_del(&swnode->entry);
@@ -1105,6 +1164,17 @@ void software_node_notify(struct device *dev)
 	if (!swnode)
 		return;
 
+	/*
+	 * When the software node is the device's secondary firmware node,
+	 * the core only records the owning device on the primary fwnode
+	 * (see device_add()). fw_devlink resolves a supplier device through
+	 * fwnode->dev, so without this a consumer referencing the software
+	 * node could never find the supplier device and would defer forever.
+	 * Make fwnode.dev point to its owner in that case.
+	 */
+	if (dev_fwnode(dev) != &swnode->fwnode && !swnode->fwnode.dev)
+		swnode->fwnode.dev = dev;
+
 	swnode_get(swnode);
 	ret = sysfs_create_link(&dev->kobj, &swnode->kobj, "software_node");
 	if (ret)
@@ -1127,6 +1197,15 @@ void software_node_notify_remove(struct device *dev)
 
 	sysfs_remove_link(&swnode->kobj, dev_name(dev));
 	sysfs_remove_link(&dev->kobj, "software_node");
+
+	/*
+	 * Drop the device pointer mirrored onto a secondary software node in
+	 * software_node_notify(). For a primary software node the core owns
+	 * fwnode->dev and clears it in device_del().
+	 */
+	if (dev_fwnode(dev) != &swnode->fwnode && swnode->fwnode.dev == dev)
+		swnode->fwnode.dev = NULL;
+
 	swnode_put(swnode);
 
 	if (swnode->managed) {

-- 
2.47.3