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>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 5ebc5d9..c66e080 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1781,6 +1781,26 @@
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 ""
diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
index e95a598..3ce5738 100644
--- a/arch/arm/boot/compressed/head.S
+++ b/arch/arm/boot/compressed/head.S
@@ -216,6 +216,59 @@
mov r10, r6
#endif
+ mov r5, #0 @ init dtb size to 0
+#ifdef CONFIG_ARM_APPENDED_DTB
+/*
+ * r0 = delta
+ * r2 = BSS start
+ * r3 = BSS end
+ * r4 = final kernel address
+ * r5 = appended dtb size (still unknown)
+ * r6 = _edata
+ * r7 = architecture ID
+ * r8 = atags/device tree pointer
+ * r9 = size of decompressed image
+ * r10 = end of this image, including bss/stack/malloc space if non XIP
+ * r11 = GOT start
+ * r12 = GOT end
+ * sp = stack pointer
+ *
+ * if there are device trees (dtb) appended to zImage, advance r10 so that the
+ * dtb data will get relocated along with the kernel if necessary.
+ */
+
+ ldr lr, [r6, #0]
+#ifndef __ARMEB__
+ ldr r1, =0xedfe0dd0 @ sig is 0xd00dfeed big endian
+#else
+ ldr r1, =0xd00dfeed
+#endif
+ cmp lr, r1
+ bne dtb_check_done @ not found
+
+ mov r8, r6 @ use the appended device tree
+
+ /* Get the dtb's size */
+ ldr r5, [r6, #4]
+#ifndef __ARMEB__
+ /* convert r5 (dtb size) to little endian */
+ eor r1, r5, r5, ror #16
+ bic r1, r1, #0x00ff0000
+ mov r5, r5, ror #8
+ eor r5, r5, r1, lsr #8
+#endif
+
+ /* preserve 64-bit alignment */
+ add r5, r5, #7
+ bic r5, r5, #7
+
+ /* relocate some pointers past the appended dtb */
+ add r6, r6, r5
+ add r10, r10, r5
+ add sp, sp, r5
+dtb_check_done:
+#endif
+
/*
* Check to see if we will overwrite ourselves.
* r4 = final kernel address
@@ -285,14 +338,16 @@
* r2 = BSS start
* r3 = BSS end
* r4 = kernel execution address
+ * r5 = appended dtb size (0 if not present)
* r7 = architecture ID
* r8 = atags pointer
* r11 = GOT start
* r12 = GOT end
* sp = stack pointer
*/
- teq r0, #0
+ orrs r1, r0, r5
beq not_relocated
+
add r11, r11, r0
add r12, r12, r0
@@ -307,12 +362,21 @@
/*
* Relocate all entries in the GOT table.
+ * Bump bss entries to _edata + dtb size
*/
1: ldr r1, [r11, #0] @ relocate entries in the GOT
- add r1, r1, r0 @ table. This fixes up the
- str r1, [r11], #4 @ C references.
+ add r1, r1, r0 @ This fixes up C references
+ cmp r1, r2 @ if entry >= bss_start &&
+ cmphs r3, r1 @ bss_end > entry
+ addhi r1, r1, r5 @ entry += dtb size
+ str r1, [r11], #4 @ next entry
cmp r11, r12
blo 1b
+
+ /* bump our bss pointers too */
+ add r2, r2, r5
+ add r3, r3, r5
+
#else
/*