[RFC 1/2] ARM:boot:device tree: Allow the device tree binary to be appended to zImage
John Bonesio
bones at secretlab.ca
Thu Jan 27 08:23:14 EST 2011
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).
Constraints:
1) A maximum 16k device tree binary is copied to memory at 0x0. If the device
tree is bigger than 16k, the kernel will probably fail ungracefully - unless
there is a device tree already embedded in the zImage.
Signed-off-by: John Bonesio <bones at secretlab.ca>
Acked-by: Grant Likely <grant.likely at secretlab.ca>
---
arch/arm/Kconfig | 7 +++++
arch/arm/boot/compressed/head.S | 52 ++++++++++++++++++++++++++++++++++++++-
2 files changed, 57 insertions(+), 2 deletions(-)
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index d8a330f..e63a441 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1593,6 +1593,13 @@ config USE_OF
help
Include support for flattened device tree machine descriptions.
+config ARM_APPENDED_DTB
+ bool "Use appended device tree blob" if OF
+ default n
+ help
+ With this option, the boot code will look for a dtb bianry
+ appended to zImage.
+
# Compressed boot loader in ROM. Yes, we really want to ask about
# TEXT and BSS so we preserve their values in the config files.
config ZBOOT_ROM_TEXT
diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
index 7193884..db860b3 100644
--- a/arch/arm/boot/compressed/head.S
+++ b/arch/arm/boot/compressed/head.S
@@ -138,7 +138,7 @@ start:
b 1f
.word 0x016f2818 @ Magic numbers to help the loader
.word start @ absolute load/run zImage address
- .word _edata @ zImage end address
+DTB: .word _edata @ zImage end address
THUMB( .thumb )
1: mov r7, r1 @ save architecture ID
mov r8, r2 @ save atags pointer
@@ -173,6 +173,9 @@ not_angel:
* by the linker here, but it should preserve r7, r8, and r9.
*/
+ /* Check if there is an appended device tree binary */
+ ldr r10, DTB @ get the address of _dtb
+
.text
adr r0, LC0
ldmia r0, {r1, r2, r3, r5, r6, r11, ip}
@@ -196,10 +199,12 @@ not_angel:
* up various pointers:
* r5 - zImage base address (_start)
* r6 - size of decompressed image
+ * r10 - zImage end
* r11 - GOT start
* ip - GOT end
*/
add r5, r5, r0
+ add r10, r10, r0
add r11, r11, r0
add ip, ip, r0
@@ -215,6 +220,7 @@ not_angel:
add r3, r3, r0
add sp, sp, r0
+
/*
* Relocate all entries in the GOT table.
*/
@@ -238,7 +244,49 @@ not_angel:
blo 1b
#endif
-not_relocated: mov r0, #0
+not_relocated:
+#ifdef CONFIG_ARM_APPENDED_DTB
+ /*
+ * Check if there is an appended device tree binary, by testing
+ * for the device tree magic signature
+ *
+ * An appended device tree will be at the end of the zImage
+ */
+ ldr r1, [r10, #0]
+ ldr r9, =0xedfe0dd0 @ sig is 0xdoodfeed stored big endian
+ cmp r1, r9
+ bne keep_atags
+
+ /* copy the device tree binary to 0x0 */
+ ldr r9, [r10, #4] @ device tree size
+
+ /* convert r9 (dtb size) to little endian */
+ eor r1, r9, r9, ror #16
+ bic r1, r1, #0x00ff0000
+ mov r9, r9, ror #8
+ eor r9, r9, r1, lsr #8
+
+ /* make sure the device tree isn't too big */
+ mov r0, #16384
+ cmp r9, r0
+ bhi keep_atags
+
+ mov r0, r2
+ mov r1, #0x0
+ add r9, r1 @ size to address from target location
+1:
+ .rept 4
+ ldmia r0!, {r10} @ relocate device tree
+ stmia r1!, {r10}
+ .endr
+ cmp r1, r9
+ blo 1b
+ mov r8, #0x0
+
+keep_atags:
+#endif
+
+__not_relocated: mov r0, #0
1: str r0, [r2], #4 @ clear bss
str r0, [r2], #4
str r0, [r2], #4
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