driver core: bus: add bus_get_dev_root() function

Instead of poking around in the struct bus_type directly for the
dev_root pointer, provide a function to return it properly reference
counted, if it is present in the bus.  This will be needed to move the
pointer out of struct bus_type in the future.

Use the function in the driver core code at the same time it is
introduced to verify that it works properly.

Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Link: https://lore.kernel.org/r/20230209093556.19132-1-gregkh@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 20 insertions, 0 deletions

diff --git a/drivers/base/bus.c b/drivers/base/bus.c
index 301b9c6ece86..def1e009ad9d 100644
--- a/drivers/base/bus.c
+++ b/drivers/base/bus.c
@@ -1334,6 +1334,26 @@ bool bus_is_registered(const struct bus_type *bus)
 	return is_initialized;
 }
 
+/**
+ * bus_get_dev_root - return a pointer to the "device root" of a bus
+ * @bus: bus to return the device root of.
+ *
+ * If a bus has a "device root" structure, return it, WITH THE REFERENCE
+ * COUNT INCREMENTED.
+ *
+ * Note, when finished with the device, a call to put_device() is required.
+ *
+ * If the device root is not present (or bus is not a valid pointer), NULL
+ * will be returned.
+ */
+struct device *bus_get_dev_root(const struct bus_type *bus)
+{
+	if (bus)
+		return get_device(bus->dev_root);
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(bus_get_dev_root);
+
 int __init buses_init(void)
 {
 	bus_kset = kset_create_and_add("bus", &bus_uevent_ops, NULL);