[PATCH 1/4] ARM:boot:device tree: Allow the device tree binary to be appended to zImage
John Bonesio
bones at secretlab.ca
Tue Mar 1 21:13:23 EST 2011
Comment/question below.
On 02/28/2011 10:39 PM, Nicolas Pitre wrote:
> On Mon, 28 Feb 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>
>
> Comments below.
>
>> ---
>>
>> arch/arm/Kconfig | 7 +++
>> arch/arm/boot/compressed/head.S | 93 ++++++++++++++++++++++++++++++++++++---
>> 2 files changed, 94 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
>> index d8a330f..68fc640 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
>
> The default is n by default, so you don't need to mention it.
>
> Also this should depend on OF (CONFIG_OF).
>
>> + help
>> + With this option, the boot code will look for a dtb bianry
>
> s/bianry/binary/
>
> Since this is an help text for people who might not have a clue about
> "dtb", it would be better to spell it out.
>
>> + 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 200625c..ae9f8c6 100644
>> --- a/arch/arm/boot/compressed/head.S
>> +++ b/arch/arm/boot/compressed/head.S
>> @@ -210,6 +210,46 @@ 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 r12, [r6, #0]
>> + ldr r1, =0xedfe0dd0 @ sig is 0xdoodfeed big endian
>> + cmp r12, r1
>> + bne dtb_check_done
>> +
>> + /* Get the dtb's size */
>> + ldr r12, [r6, #4] @ device tree size
>> +
>> + /* convert r12 (dtb size) to little endian */
>> + eor r1, r12, r12, ror #16
>> + bic r1, r1, #0x00ff0000
>> + mov r12, r12, ror #8
>> + eor r12, r12, r1, lsr #8
>> +
>> + add r10, r10, r12
>> + add r6, r6, r12
>> +
>> +dtb_check_done:
>> + adr r1, LC0
>> + ldr r12, [r1, #28] @ restore r12 (GOT end)
>> +#endif
>
> Instead of clobbering r12, you could use lr instead.
>
> The byte swap on the size should be done only if __ARMEB__ is not
> defined i.e. #ifndef __ARMEB__ ...
>
> Also the DT signature should be endian aware.
>
>> /*
>> * Check to see if we will overwrite ourselves.
>> @@ -223,8 +263,8 @@ restart: adr r0, LC0
>> */
>> cmp r4, r10
>> bhs wont_overwrite
>> - add r10, r4, r9
>> - cmp r10, r5
>> + add r1, r4, r9
>> + cmp r1, r5
>> bls wont_overwrite
>>
>> /*
>> @@ -272,8 +312,10 @@ wont_overwrite:
>> * r12 = GOT end
>> * sp = stack pointer
>> */
>> - teq r0, #0
>> - beq not_relocated
>> + adr r1, LC0
>> + ldr r6, [r1, #16] @ reload _edata value
>
> Why?
>
>> +
>> + add r6, r6, r0
>> add r11, r11, r0
>> add r12, r12, r0
>>
>> @@ -288,12 +330,34 @@ wont_overwrite:
>>
>> /*
>> * Relocate all entries in the GOT table.
>> + * Bump bss entries to past image end (r10)
>> */
>> + sub r5, r10, r6 @ delta of image end and _edata
>> + add r5, r5, #7 @ ... rounded up to a multiple
>> + bic r5, r5, #7 @ ... of 8 bytes, so misaligned
>> + @ ... GOT entry doesn't
>> + @ ... overwrite end of image
>
> This is wrong. You are going to displace the .bss pointers even if they
> don't need that in the case where no dtb was found. And if a dtb was
> found the displacement is going to be the size of the dtb _plus_ the
> size of the .bss_stack instead of only the dtb size.
>
> At this point you should only keep track of the .bss displacement in
> addition to the delta offset in r0. And if both are equal to zero then
> skip over the fixup loop as before.
Maybe I'm not understanding correctly. I think that if there is an
appended dtb, then there are sections like the code and data that needs
to be adjusted by the old r0 value, while the bss and the stack need to
be adjusted by the old r0 + dtb size.
If my understanding is right, then we can't just add the dtb size to r0
and adjust everything.
Am I missing something?
>
>> 1: ldr r1, [r11, #0] @ relocate entries in the GOT
>> add r1, r1, r0 @ table. This fixes up the
>> + cmp r1, r2
>> + movcc r9, #0 @ r9 = entry < bss_start ? 0 :
>> + movcs r9, #1 @ 1;
>> + cmp r1, r3
>> + movcs r9, #0 @ r9 = entry >= end ? 0 : t1;
>> + cmp r9, #0
>> + addne r1, r5 @ entry += r9 ? bss delta : 0;
>
> The above would be much more elegant if written like this:
>
> cmp r1, r2
> cmphs r3, r1
> addhi r1, r5
>
>> str r1, [r11], #4 @ C references.
>> cmp r11, r12
>> blo 1b
>> +
>> + /* bump our bss registers too */
>> + add r2, r2, r5
>> + add r3, r3, r5
>> +
>> + /* bump the stack pinter, if at or above _edata */
>> + cmp sp, r6
>> + addcs sp, sp, r5
>
> This will always be true as this is within #ifndef CONFIG_ZBOOT_ROM.
>
>> #else
>>
>> /*
>> @@ -309,7 +373,7 @@ wont_overwrite:
>> blo 1b
>> #endif
>>
>> -not_relocated: mov r0, #0
>> + mov r0, #0
>> 1: str r0, [r2], #4 @ clear bss
>> str r0, [r2], #4
>> str r0, [r2], #4
>> @@ -317,8 +381,25 @@ not_relocated: mov r0, #0
>> cmp r2, r3
>> blo 1b
>>
>> +#ifdef CONFIG_ARM_APPENDED_DTB
>> +/*
>> + * The C runtime environment should now be set up sufficiently.
>> + * r4 = kernel execution address
>> + * r6 = _edata
>> + * r7 = architecture ID
>> + * r8 = atags pointer
>> + *
>> + * if there is a device tree (dtb) appended to zImage, set up to use this dtb.
>> + */
>> + ldr r0, [r6, #0]
>> + ldr r1, =0xedfe0dd0 @ sig is 0xdoodfeed big endian
>> + cmp r0, r1
>> + bne keep_atags
>> +
>> + mov r8, r6 @ use the appended device tree
>
> You should have updated r8 the moment you knew you have a valid dtb
> earlier instead of duplicating this test here.
>
>> +keep_atags:
>> +#endif
>> /*
>> - * The C runtime environment should now be setup sufficiently.
>> * Set up some pointers, and start decompressing.
>> * r4 = kernel execution address
>> * r7 = architecture ID
>>
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