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>
diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
index ba5c552..9f5ac11 100644
--- a/arch/arm/boot/compressed/head.S
+++ b/arch/arm/boot/compressed/head.S
@@ -246,6 +246,38 @@
cmp lr, r1
bne dtb_check_done @ not found
+#ifdef CONFIG_ARM_ATAG_DTB_COMPAT
+ /*
+ * OK... Let's do some funky business here.
+ * If we do have a DTB appended to zImage, and we do have
+ * an ATAG list around, we want the later to be translated
+ * and folded into the former here. To be on the safe side,
+ * let's temporarily move the stack away into the malloc
+ * area. No GOT fixup has occurred yet, but none of the
+ * code we're about to call uses any global variable.
+ */
+ add sp, sp, #0x10000
+ stmfd sp!, {r0-r3, ip, lr}
+ mov r0, r8
+ mov r1, r6
+ sub r2, sp, r6
+ bl atags_to_fdt
+
+ /*
+ * If returned value is 1, there is no ATAG at the location
+ * pointed by r8. Try the typical 0x100 offset from start
+ * of RAM and hope for the best.
+ */
+ cmp r0, #1
+ sub r0, r4, #(TEXT_OFFSET - 0x100)
+ mov r1, r6
+ sub r2, sp, r6
+ blne atags_to_fdt
+
+ ldmfd sp!, {r0-r3, ip, lr}
+ sub sp, sp, #0x10000
+#endif
+
mov r8, r6 @ use the appended device tree
/*