Re: [PATCH 2/3] ARM: zImage: Allow the appending of a device tree binary

[Grant Likely <grant.likely@secretlab.ca>]

On Sun, Jun 12, 2011 at 02:06:39AM -0400, Nicolas Pitre wrote:
> From: John Bonesio <bones@secretlab.ca>
> 
> 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: adjusted to latest zImage changes plus additional cleanups]
> Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>

Acked-by: Grant Likely <grant.likely@secretlab.ca>

> ---
>  arch/arm/Kconfig                |    8 ++++
>  arch/arm/boot/compressed/head.S |   70 +++++++++++++++++++++++++++++++++++++--
>  2 files changed, 75 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 9adc278..66b7d1e 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -1727,6 +1727,14 @@ config ZBOOT_ROM_MMCIF
>  	  which in turn loads the rest the kernel image to RAM using the
>  	  MMCIF hardware block.
>  
> +config ARM_APPENDED_DTB
> +	bool "Use appended device tree blob to zImage"
> +	depends on OF && !ZBOOT_ROM
> +	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).
> +
>  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 f9da419..4bc009c 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 lr (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
>  
>  		/*
> -- 
> 1.7.4
>