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 <[email protected]> Acked-by: Grant Likely <[email protected]> --- 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 _______________________________________________ devicetree-discuss mailing list [email protected] https://lists.ozlabs.org/listinfo/devicetree-discuss
