[PATCH net-next 07/15] mfd: core: add ability for cells to probe on a custom parent OF node

[Vladimir Oltean]

I would like the "nxp,sja1110a" driver, in the configuration below, to
be able to probe the drivers for "nxp,sja1110-base-t1-mdio" and for
"nxp,sja1110-base-tx-mdio" via mfd_add_devices():

	ethernet-switch@0 {
		compatible = "nxp,sja1110a";

		mdios {
			mdio@0 {
				compatible = "nxp,sja1110-base-t1-mdio";
			};

			mdio@1 {
				compatible = "nxp,sja1110-base-tx-mdio";
			};
		};
	};

This isn't currently possible, because mfd assumes that the parent
OF node ("mdios") == OF node of the parent ("ethernet-switch@0"), which
in this case isn't true, and as it searches through the children of
"ethernet-switch@0", it finds no MDIO bus to probe.

Cc: Lee Jones <lee@xxxxxxxxxx>
Signed-off-by: Vladimir Oltean <vladimir.oltean@xxxxxxx>
---
 drivers/mfd/mfd-core.c   | 11 +++++++++--
 include/linux/mfd/core.h |  7 +++++++
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/mfd/mfd-core.c b/drivers/mfd/mfd-core.c
index 7d14a1e7631e..e0b7f93a2654 100644
--- a/drivers/mfd/mfd-core.c
+++ b/drivers/mfd/mfd-core.c
@@ -181,8 +181,14 @@ static int mfd_add_device(struct device *parent, int id,
 	if (ret < 0)
 		goto fail_res;
 
-	if (IS_ENABLED(CONFIG_OF) && parent->of_node && cell->of_compatible) {
-		for_each_child_of_node(parent->of_node, np) {
+	if (IS_ENABLED(CONFIG_OF)) {
+		const struct device_node *parent_of_node;
+
+		parent_of_node = cell->parent_of_node ?: parent->of_node;
+		if (!parent_of_node || !cell->of_compatible)
+			goto skip_of;
+
+		for_each_child_of_node(parent_of_node, np) {
 			if (of_device_is_compatible(np, cell->of_compatible)) {
 				/* Skip 'disabled' devices */
 				if (!of_device_is_available(np)) {
@@ -213,6 +219,7 @@ static int mfd_add_device(struct device *parent, int id,
 				cell->name, platform_id);
 	}
 
+skip_of:
 	mfd_acpi_add_device(cell, pdev);
 
 	if (cell->pdata_size) {
diff --git a/include/linux/mfd/core.h b/include/linux/mfd/core.h
index faeea7abd688..2e94ea376125 100644
--- a/include/linux/mfd/core.h
+++ b/include/linux/mfd/core.h
@@ -81,6 +81,13 @@ struct mfd_cell {
 	/* Software node for the device. */
 	const struct software_node *swnode;
 
+	/*
+	 * Parent OF node of the device, if different from the OF node
+	 * of the MFD parent (e.g. there is at least one more hierarchical
+	 * level between them)
+	 */
+	const struct device_node *parent_of_node;
+
 	/*
 	 * Device Tree compatible string
 	 * See: Documentation/devicetree/usage-model.rst Chapter 2.2 for details
-- 
2.34.1