ARM: zImage: Allow the appending of a device tree binary

This patch provides the ability to boot using a device tree that is appended
to the raw binary zImage (e.g. cat zImage <filename>.dtb > zImage_w_dtb).

Signed-off-by: John Bonesio <bones@secretlab.ca>
[nico: ported to latest zImage changes plus additional cleanups/improvements]
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Tony Lindgren <tony@atomide.com>
Tested-by: Shawn Guo <shawn.guo@linaro.org>
Tested-by: Dave Martin <dave.martin@linaro.org>
Tested-by: Thomas Abraham <thomas.abraham@linaro.org>

1 files changed, 20 insertions, 0 deletions

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 5ebc5d922ea1..c66e0808c2b1 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1781,6 +1781,26 @@ config ZBOOT_ROM_SH_MOBILE_SDHI
 
 endchoice
 
+config ARM_APPENDED_DTB
+        bool "Use appended device tree blob to zImage (EXPERIMENTAL)"
+        depends on OF && !ZBOOT_ROM && EXPERIMENTAL
+        help
+          With this option, the boot code will look for a device tree binary
+          (DTB) appended to zImage
+          (e.g. cat zImage <filename>.dtb > zImage_w_dtb).
+
+          This is meant as a backward compatibility convenience for those
+          systems with a bootloader that can't be upgraded to accommodate
+          the documented boot protocol using a device tree.
+
+          Beware that there is very little in terms of protection against
+          this option being confused by leftover garbage in memory that might
+          look like a DTB header after a reboot if no actual DTB is appended
+          to zImage.  Do not leave this option active in a production kernel
+          if you don't intend to always append a DTB.  Proper passing of the
+          location into r2 of a bootloader provided DTB is always preferable
+          to this option.
+
 config CMDLINE
         string "Default kernel command string"
         default ""