kbuild: add target to build a cpio containing modules

Add a new package target to build a cpio archive containing the kernel
modules. This is particularly useful to supplement an existing initramfs
with the kernel modules so that the root filesystem can be started with
all needed kernel modules without modifying it.

Signed-off-by: Sascha Hauer <[email protected]>
Reviewed-by: Simon Glass <[email protected]>
Tested-by: Simon Glass <[email protected]>
Co-developed-by: Ahmad Fatoum <[email protected]>
Signed-off-by: Ahmad Fatoum <[email protected]>
Reviewed-by: Thomas Weißschuh <[email protected]>
Reviewed-by: Nathan Chancellor <[email protected]>
Tested-by: Nathan Chancellor <[email protected]>
Tested-by: Nicolas Schier <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Nicolas Schier <[email protected]>

Author: saschahauer

scripts/Makefile.package

@@ -189,6 +189,25 @@ tar-pkg: linux-$(KERNELRELEASE)-$(ARCH).tar
 tar%-pkg: linux-$(KERNELRELEASE)-$(ARCH).tar.% FORCE
 	@:
 
+# modules-cpio-pkg - generate an initramfs with the modules
+# ---------------------------------------------------------------------------
+
+.tmp_modules_cpio: FORCE
+	$(Q)$(MAKE) -f $(srctree)/Makefile
+	$(Q)rm -rf $@
+	$(Q)$(MAKE) -f $(srctree)/Makefile INSTALL_MOD_PATH=$@ modules_install
+
+quiet_cmd_cpio = CPIO    $@
+      cmd_cpio = $(CONFIG_SHELL) $(srctree)/usr/gen_initramfs.sh -o $@ $<
+
+modules-$(KERNELRELEASE)-$(ARCH).cpio: .tmp_modules_cpio
+	$(Q)$(MAKE) $(build)=usr usr/gen_init_cpio
+	$(call cmd,cpio)
+
+PHONY += modules-cpio-pkg
+modules-cpio-pkg: modules-$(KERNELRELEASE)-$(ARCH).cpio
+	@:
+
 # perf-tar*-src-pkg - generate a source tarball with perf source
 # ---------------------------------------------------------------------------
 
@@ -245,6 +264,7 @@ help:
 	@echo '  tarbz2-pkg          - Build the kernel as a bzip2 compressed tarball'
 	@echo '  tarxz-pkg           - Build the kernel as a xz compressed tarball'
 	@echo '  tarzst-pkg          - Build the kernel as a zstd compressed tarball'
+	@echo '  modules-cpio-pkg    - Build the kernel modules as cpio archive'
 	@echo '  perf-tar-src-pkg    - Build the perf source tarball with no compression'
 	@echo '  perf-targz-src-pkg  - Build the perf source tarball with gzip compression'
 	@echo '  perf-tarbz2-src-pkg - Build the perf source tarball with bz2 compression'