kbuild: correct and clarify versioning info in Makefile

The attached patch clarifies the creation of KERNELRELEASE and
corrects an error regarding the use of $(LOCALVERSION).

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

1 files changed, 27 insertions, 5 deletions

diff --git a/Makefile b/Makefile
index 13bc589c6056..241fed3a74a6 100644
--- a/Makefile
+++ b/Makefile
@@ -760,12 +760,34 @@ $(vmlinux-dirs): prepare scripts
         $(Q)$(MAKE) $(build)=$@
 
 # Build the kernel release string
-# The KERNELRELEASE is stored in a file named include/config/kernel.release
-# to be used when executing for example make install or make modules_install
 #
-# Take the contents of any files called localversion* and the config
-# variable CONFIG_LOCALVERSION and append them to KERNELRELEASE.
-# LOCALVERSION from the command line override all of this
+# The KERNELRELEASE value built here is stored in the file
+# include/config/kernel.release, and is used when executing several
+# make targets, such as "make install" or "make modules_install."
+#
+# The eventual kernel release string consists of the following fields,
+# shown in a hierarchical format to show how smaller parts are concatenated
+# to form the larger and final value, with values coming from places like
+# the Makefile, kernel config options, make command line options and/or
+# SCM tag information.
+#
+#       $(KERNELVERSION)
+#         $(VERSION)                    eg, 2
+#         $(PATCHLEVEL)                 eg, 6
+#         $(SUBLEVEL)                   eg, 18
+#         $(EXTRAVERSION)               eg, -rc6
+#       $(localver-full)
+#         $(localver)
+#           localversion*               (all localversion* files)
+#           $(CONFIG_LOCALVERSION)      (from kernel config setting)
+#         $(localver-auto)              (only if CONFIG_LOCALVERSION_AUTO is set)
+#           ./scripts/setlocalversion   (SCM tag, if one exists)
+#           $(LOCALVERSION)             (from make command line if provided)
+#
+#  Note how the final $(localver-auto) string is included *only* if the
+# kernel config option CONFIG_LOCALVERSION_AUTO is selected.  Also, at the
+# moment, only git is supported but other SCMs can edit the script
+# scripts/setlocalversion and add the appropriate checks as needed.
 
 nullstring :=
 space      := $(nullstring) # end of line