[PATCH] ARM:boot:device tree: Allow the device tree binary to be appended to zImage
Nicolas Pitre
nico at fluxnic.net
Thu Mar 17 14:42:39 EDT 2011
On Wed, 9 Mar 2011, John Bonesio wrote:
> 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 at secretlab.ca>
You're almost there, but there are still remaining issues with this
patch.
> ---
>
> arch/arm/Kconfig | 7 ++++
> arch/arm/boot/compressed/head.S | 75 +++++++++++++++++++++++++++++++++++++--
> 2 files changed, 79 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index d8a330f..1a55e3e 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"
> + depends on OF
> + help
> + With this option, the boot code will look for a device tree binary
> + (dtb) appended to zImage.
> +
I'd put this option below the ZBOOT_ROM option, and make it dependent on
!ZBOOT_ROM, e.g.:
depends on OF && !ZBOOT_ROM
> diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
> index 200625c..611719e 100644
> --- a/arch/arm/boot/compressed/head.S
> +++ b/arch/arm/boot/compressed/head.S
> @@ -210,6 +210,58 @@ restart: adr r0, LC0
> */
> mov r10, r6
> #endif
> +#ifdef CONFIG_ARM_APPENDED_DTB
> +/*
> + * r0 = delta
> + * r2 = BSS start
> + * r3 = BSS end
> + * r4 = final kernel address
> + * r5 = start of this image
> + * 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
> + *
> + * 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
> +
> + mov r8, r6 @ use the appended device tree
> +
> + /* Get the dtb's size */
> + ldr lr, [r6, #4]
> +
> +#ifndef __ARMEB__
> + /* convert lr (dtb size) to little endian */
> + eor r1, lr, lr, ror #16
> + bic r1, r1, #0x00ff0000
> + mov lr, lr, ror #8
> + eor lr, lr, r1, lsr #8
> +#endif
> + /*
> + * dtb size rounded up to a multiple of 8 bytes so a
> + * misaligned GOT entry doesn't cause the end of the
> + * dtb binary to be overwritten.
> + */
> + add lr, lr, #7
> + bic lr, lr, #7
> +
> + add r10, r10, lr
> + add r6, r6, lr
> +dtb_check_done:
> +#endif
Now if no dtb was found, or if that code is not configured, then lr
contains garbage and that may have random consequences with the code
that follows, which would explain the reported bad behaviors with this
patch applied even if not configured in the kernel.
> /*
> * Check to see if we will overwrite ourselves.
> @@ -272,7 +324,8 @@ wont_overwrite:
> * r12 = GOT end
> * sp = stack pointer
> */
> - teq r0, #0
> + add r1, r0, lr
> + teq r1, #0
> beq not_relocated
A better way to write the above is simply:
orrs r1, r0, lr
beq not_relocated
> add r11, r11, r0
> add r12, r12, r0
> @@ -288,12 +341,28 @@ 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, lr @ entry += dtb size
> + str r1, [r11], #4 @ next entry
> cmp r11, r12
> blo 1b
> +
> + /* bump our bss registers too */
> + add r2, r2, lr
> + add r3, r3, lr
> +
> + /*
> + * bump the stack pinter
> + *
> + * If the linker script changes so the stack is not after
> + * the bss section, this code will be wrong.
> + */
> + add sp, sp, lr
> #else
>
> /*
>
Nicolas
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