ARM: zImage: allow supplementing appended DTB with traditional ATAG data

Some old bootloaders can't be updated to a device tree capable one,
yet they provide ATAGs with memory configuration, the ramdisk address,
the kernel cmdline string, etc.  To allow a device tree enabled
kernel to be used with such bootloaders, it is necessary to convert those
ATAGs into FDT properties and fold them into the DTB appended to zImage.

Currently the following ATAGs are converted:

	ATAG_CMDLINE
	ATAG_MEM
	ATAG_INITRD2

If the corresponding information already exists in the appended DTB, it
is replaced, otherwise the required node is created to hold it.

The code looks for ATAGs at the location pointed by the value of r2 upon
entry into the zImage code.  If no ATAGs are found there, an attempt at
finding ATAGs at the typical 0x100 offset from start of RAM is made.
Otherwise the DTB is left unchanged.

Thisstarted from an older patch from John Bonesio <bones@secretlab.ca>,
with contributions from David Brown <davidb@codeaurora.org>.

Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
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, 12 insertions, 0 deletions

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index c66e0808c2b1..73c320ea172c 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1801,6 +1801,18 @@ config ARM_APPENDED_DTB
           location into r2 of a bootloader provided DTB is always preferable
           to this option.
 
+config ARM_ATAG_DTB_COMPAT
+        bool "Supplement the appended DTB with traditional ATAG information"
+        depends on ARM_APPENDED_DTB
+        help
+          Some old bootloaders can't be updated to a DTB capable one, yet
+          they provide ATAGs with memory configuration, the ramdisk address,
+          the kernel cmdline string, etc.  Such information is dynamically
+          provided by the bootloader and can't always be stored in a static
+          DTB.  To allow a device tree enabled kernel to be used with such
+          bootloaders, this option allows zImage to extract the information
+          from the ATAG list and store it at run time into the appended DTB.
+
 config CMDLINE
         string "Default kernel command string"
         default ""