powerpc/powernv: move to use bus_get_dev_root()

Direct access to the struct bus_type dev_root pointer is going away soon
so replace that with a call to bus_get_dev_root() instead, which is what
it is there for.

Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Wolfram Sang <wsa+renesas@sang-engineering.com>
Cc: Joel Stanley <joel@jms.id.au>
Cc: Liang He <windhl@126.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Julia Lawall <Julia.Lawall@inria.fr>
Cc: linuxppc-dev@lists.ozlabs.org
Link: https://lore.kernel.org/r/20230313182918.1312597-13-gregkh@linuxfoundation.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/powerpc/platforms/powernv/idle.c

@@ -1464,14 +1464,19 @@ static int __init pnv_init_idle_states(void)
 			power7_fastsleep_workaround_entry = false;
 			power7_fastsleep_workaround_exit = false;
 		} else {
+			struct device *dev_root;
 			/*
 			 * OPAL_PM_SLEEP_ENABLED_ER1 is set. It indicates that
 			 * workaround is needed to use fastsleep. Provide sysfs
 			 * control to choose how this workaround has to be
 			 * applied.
 			 */
-			device_create_file(cpu_subsys.dev_root,
+			dev_root = bus_get_dev_root(&cpu_subsys);
+			if (dev_root) {
+				device_create_file(dev_root,
 						   &dev_attr_fastsleep_workaround_applyonce);
+				put_device(dev_root);
+			}
 		}
 
 		update_subcore_sibling_mask();

arch/powerpc/platforms/powernv/subcore.c

@@ -415,7 +415,9 @@ static DEVICE_ATTR(subcores_per_core, 0644,
 
 static int subcore_init(void)
 {
+	struct device *dev_root;
 	unsigned pvr_ver;
+	int rc = 0;
 
 	pvr_ver = PVR_VER(mfspr(SPRN_PVR));
 
@@ -435,7 +437,11 @@ static int subcore_init(void)
 
 	set_subcores_per_core(1);
 
-	return device_create_file(cpu_subsys.dev_root,
-				  &dev_attr_subcores_per_core);
+	dev_root = bus_get_dev_root(&cpu_subsys);
+	if (dev_root) {
+		rc = device_create_file(dev_root, &dev_attr_subcores_per_core);
+		put_device(dev_root);
+	}
+	return rc;
 }
 machine_device_initcall(powernv, subcore_init);