Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/drivers/dax/Kconfig b/drivers/dax/Kconfig
index e0700bf..f33c73e 100644
--- a/drivers/dax/Kconfig
+++ b/drivers/dax/Kconfig
@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0-only
 config DAX_DRIVER
 	select DAX
 	bool
@@ -29,6 +30,31 @@
 	  driver consumes memory ranges allocated and exported by the
 	  libnvdimm sub-system.
 
-	  Say Y if unsure
+	  Say M if unsure
+
+config DEV_DAX_KMEM
+	tristate "KMEM DAX: volatile-use of persistent memory"
+	default DEV_DAX
+	depends on DEV_DAX
+	depends on MEMORY_HOTPLUG # for add_memory() and friends
+	help
+	  Support access to persistent memory as if it were RAM.  This
+	  allows easier use of persistent memory by unmodified
+	  applications.
+
+	  To use this feature, a DAX device must be unbound from the
+	  device_dax driver (PMEM DAX) and bound to this kmem driver
+	  on each boot.
+
+	  Say N if unsure.
+
+config DEV_DAX_PMEM_COMPAT
+	tristate "PMEM DAX: support the deprecated /sys/class/dax interface"
+	depends on m && DEV_DAX_PMEM=m
+	default DEV_DAX_PMEM
+	help
+	  Older versions of the libdaxctl library expect to find all
+	  device-dax instances under /sys/class/dax. If libdaxctl in
+	  your distribution is older than v58 say M, otherwise say N.
 
 endif