[PATCH v6] i2c: mux: Propagate software nodes to channel adapters

[Ahmad Byagowi]

Device Tree channel nodes are associated with the adapters created by
i2c-mux, but equivalent software-node descriptions are not.

When the mux device has a primary software node, find the child whose
reg value matches the channel and use it as the new adapter firmware node.
Keep the node reference through child-client removal and release it after
adapter deletion.

Also balance the Device Tree channel-node reference when adapter
registration fails.

Signed-off-by: Ahmad Byagowi <ahmadexp@xxxxxxxxx>
---
Changes since v5:
  - Send the I2C prerequisite as a standalone patch for the I2C tree.
  - Limit propagation to mux devices with a primary software node.
  - Avoid secondary-fwnode access and changes to generic adapter lookup.
  - Follow the i2c-atr reference-lifetime pattern for channel nodes.
  - Balance the Device Tree channel reference on adapter-add failure.
  - Rebase onto the I2C i2c-next branch.

v5: https://lore.kernel.org/r/cover.1786746757.git.ahmadexp@xxxxxxxxx/
---
 drivers/i2c/i2c-mux.c | 61 +++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 59 insertions(+), 2 deletions(-)

diff --git a/drivers/i2c/i2c-mux.c b/drivers/i2c/i2c-mux.c
index 681a201c239ba..76fa89dc6a222 100644
--- a/drivers/i2c/i2c-mux.c
+++ b/drivers/i2c/i2c-mux.c
@@ -25,6 +25,7 @@
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/of.h>
+#include <linux/property.h>
 #include <linux/slab.h>
 #include <linux/sysfs.h>
 
@@ -33,6 +34,7 @@ struct i2c_mux_priv {
 	struct i2c_adapter adap;
 	struct i2c_algorithm algo;
 	struct i2c_mux_core *muxc;
+	struct fwnode_handle *swnode;
 	u32 chan_id;
 };
 
@@ -264,6 +266,49 @@ static const struct i2c_lock_operations i2c_parent_lock_ops = {
 	.unlock_bus =  i2c_parent_unlock_bus,
 };
 
+static struct fwnode_handle *
+i2c_mux_get_channel_swnode(struct i2c_mux_core *muxc, u32 chan_id)
+{
+	struct fwnode_handle *dev_node = dev_fwnode(muxc->dev);
+	struct fwnode_handle *mux_node, *child = NULL;
+	u32 reg;
+
+	if (!is_software_node(dev_node))
+		return NULL;
+
+	if (muxc->arbitrator)
+		mux_node = fwnode_get_named_child_node(dev_node, "i2c-arb");
+	else if (muxc->gate)
+		mux_node = fwnode_get_named_child_node(dev_node, "i2c-gate");
+	else
+		mux_node = fwnode_get_named_child_node(dev_node, "i2c-mux");
+
+	if (mux_node) {
+		/* A "reg" property indicates an old-style firmware entry. */
+		if (!fwnode_property_read_u32(mux_node, "reg", &reg)) {
+			fwnode_handle_put(mux_node);
+			mux_node = NULL;
+		}
+	}
+
+	if (!mux_node)
+		mux_node = fwnode_handle_get(dev_node);
+	else if (muxc->arbitrator || muxc->gate)
+		child = fwnode_handle_get(mux_node);
+
+	if (!child) {
+		fwnode_for_each_child_node(mux_node, child) {
+			if (fwnode_property_read_u32(child, "reg", &reg))
+				continue;
+			if (chan_id == reg)
+				break;
+		}
+	}
+
+	fwnode_handle_put(mux_node);
+	return child;
+}
+
 int i2c_mux_add_adapter(struct i2c_mux_core *muxc,
 			u32 force_nr, u32 chan_id)
 {
@@ -324,8 +369,8 @@ int i2c_mux_add_adapter(struct i2c_mux_core *muxc,
 		priv->adap.lock_ops = &i2c_parent_lock_ops;
 
 	/*
-	 * Try to populate the mux adapter's of_node, expands to
-	 * nothing if !CONFIG_OF.
+	 * Associate the mux adapter with its DT or software-node channel.
+	 * DT support expands to nothing if !CONFIG_OF.
 	 */
 	if (muxc->dev->of_node) {
 		struct device_node *dev_node = muxc->dev->of_node;
@@ -364,6 +409,10 @@ int i2c_mux_add_adapter(struct i2c_mux_core *muxc,
 
 		priv->adap.dev.of_node = child;
 		of_node_put(mux_node);
+	} else {
+		priv->swnode = i2c_mux_get_channel_swnode(muxc, chan_id);
+		if (priv->swnode)
+			device_set_node(&priv->adap.dev, priv->swnode);
 	}
 
 	/*
@@ -408,6 +457,8 @@ int i2c_mux_add_adapter(struct i2c_mux_core *muxc,
 	return 0;
 
 err_free_priv:
+	fwnode_handle_put(priv->swnode);
+	of_node_put(priv->adap.dev.of_node);
 	kfree(priv);
 	return ret;
 }
@@ -429,7 +480,13 @@ void i2c_mux_del_adapters(struct i2c_mux_core *muxc)
 		sysfs_remove_link(&muxc->dev->kobj, symlink_name);
 
 		sysfs_remove_link(&priv->adap.dev.kobj, "mux_device");
+		/*
+		 * Keep the software node through child removal. The adapter
+		 * device is cleared on deletion, so release the saved reference
+		 * afterwards.
+		 */
 		i2c_del_adapter(adap);
+		fwnode_handle_put(priv->swnode);
 		of_node_put(np);
 		kfree(priv);
 	}

base-commit: b0e590bb83a9e40dc1e77a2c82d7f3e670fb74b3
-- 
2.50.1 (Apple Git-155)