powerpc/bootwrapper: Add documentation of boot wrapper targets

There have been many questions on and off the mailing list about how
exactly the bootwrapper is used for embedded targets.  Add some
documentation and help text to try and clarify the system.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

1 files changed, 14 insertions, 1 deletions

diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index 59ae7d9cdcc..9155c9312c1 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -163,12 +163,25 @@ bootwrapper_install %.dtb:
 	$(Q)$(MAKE) ARCH=ppc64 $(build)=$(boot) $(patsubst %,$(boot)/%,$@)
 
 define archhelp
-  @echo '* zImage          - Compressed kernel image (arch/$(ARCH)/boot/zImage.*)'
+  @echo '* zImage          - Build default images selected by kernel config'
+  @echo '  zImage.*        - Compressed kernel image (arch/$(ARCH)/boot/zImage.*)'
+  @echo '  uImage          - U-Boot native image format'
+  @echo '  cuImage.<dt>    - Backwards compatible U-Boot image for older'
+  @echo '                    versions which do not support device trees'
+  @echo '  dtbImage.<dt>   - zImage with an embedded device tree blob'
+  @echo '  simpleImage.<dt> - Firmware independent image.'
+  @echo '  treeImage.<dt>  - Support for older IBM 4xx firmware (not U-Boot)'
   @echo '  install         - Install kernel using'
   @echo '                    (your) ~/bin/installkernel or'
   @echo '                    (distribution) /sbin/installkernel or'
   @echo '                    install to $$(INSTALL_PATH) and run lilo'
   @echo '  *_defconfig     - Select default config from arch/$(ARCH)/configs'
+  @echo ''
+  @echo '  Targets with <dt> embed a device tree blob inside the image'
+  @echo '  These targets support board with firmware that does not'
+  @echo '  support passing a device tree directly.  Replace <dt> with the'
+  @echo '  name of a dts file from the arch/$(ARCH)/boot/dts/ directory'
+  @echo '  (minus the .dts extension).'
 endef
 
 install: