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>

2 files changed, 87 insertions, 3 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 ""
diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
index e95a5989602a..3ce5738ddb98 100644
--- a/arch/arm/boot/compressed/head.S
+++ b/arch/arm/boot/compressed/head.S
@@ -216,6 +216,59 @@ restart:	adr	r0, LC0
                 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 @@ wont_overwrite:
  *   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 @@ wont_overwrite:
 
                 /*
                  * 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
 
                 /*