software node: allow referencing firmware nodes

At the moment software nodes can only reference other software nodes.
This is a limitation for devices created, for instance, on the auxiliary
bus with a dynamic software node attached which cannot reference devices
the firmware node of which is "real" (as an OF node or otherwise).

Make it possible for a software node to reference all firmware nodes in
addition to static software nodes. To that end: add a second pointer to
struct software_node_ref_args of type struct fwnode_handle. The core
swnode code will first check the swnode pointer and if it's NULL, it
will assume the fwnode pointer should be set.

Software node graphs remain the same, as in: the remote endpoints still
have to be software nodes.

Acked-by: Linus Walleij <[e-mail]>
Reviewed-by: Sakari Ailus <[e-mail]>
Reviewed-by: Andy Shevchenko <[e-mail]>
Acked-by: Greg Kroah-Hartman <[e-mail]>
Signed-off-by: Bartosz Golaszewski <[e-mail]>
Reviewed-by: Charles Keepax <[e-mail]>
Tested-by: Charles Keepax <[e-mail]>
Signed-off-by: Philipp Zabel <[e-mail]>

drivers/base/swnode.c

···
 	ref_array = prop->pointer;
 	ref = &ref_array[index];
 
-	refnode = software_node_fwnode(ref->node);
+	/*
+	 * A software node can reference other software nodes or firmware
+	 * nodes (which are the abstraction layer sitting on top of them).
+	 * This is done to ensure we can create references to static software
+	 * nodes before they're registered with the firmware node framework.
+	 * At the time the reference is being resolved, we expect the swnodes
+	 * in question to already have been registered and to be backed by
+	 * a firmware node. This is why we use the fwnode API below to read the
+	 * relevant properties and bump the reference count.
+	 */
+
+	if (ref->swnode)
+		refnode = software_node_fwnode(ref->swnode);
+	else if (ref->fwnode)
+		refnode = ref->fwnode;
+	else
+		return -EINVAL;
+
 	if (!refnode)
 		return -ENOENT;
 
···
 
 	ref = prop->pointer;
 
-	return software_node_get(software_node_fwnode(ref[0].node));
+	if (!ref->swnode)
+		return NULL;
+
+	return software_node_get(software_node_fwnode(ref->swnode));
 }
 
 static struct fwnode_handle *

include/linux/property.h

···
 
 /**
  * struct software_node_ref_args - Reference property with additional arguments
- * @node: Reference to a software node
+ * @swnode: Reference to a software node
+ * @fwnode: Alternative reference to a firmware node handle
  * @nargs: Number of elements in @args array
  * @args: Integer arguments
  */
 struct software_node_ref_args {
-	const struct software_node *node;
+	const struct software_node *swnode;
+	struct fwnode_handle *fwnode;
 	unsigned int nargs;
 	u64 args[NR_FWNODE_REFERENCE_ARGS];
 };
 
 #define SOFTWARE_NODE_REFERENCE(_ref_, ...)			\
 (const struct software_node_ref_args) {				\
-	.node = _ref_,						\
+	.swnode = _Generic(_ref_,				\
+			   const struct software_node *: _ref_,	\
+			   default: NULL),			\
+	.fwnode = _Generic(_ref_,				\
+			   struct fwnode_handle *: _ref_,	\
+			   default: NULL),			\
 	.nargs = COUNT_ARGS(__VA_ARGS__),			\
 	.args = { __VA_ARGS__ },				\
 }