[PATCH 1/2] of: Add support for linking device tree blobs into vmlinux

[Grant Likely]

On Mon, Nov 15, 2010 at 10:28 PM, Dirk Brandewie
<dirk.brandewie at gmail.com> wrote:
> On 11/15/2010 09:17 PM, Grant Likely wrote:
>>
>> On Mon, Nov 15, 2010 at 10:06 PM, Dirk Brandewie
>> <dirk.brandewie at gmail.com>  wrote:
>>>
>>> On 11/15/2010 08:41 PM, Grant Likely wrote:
>>>>
>>>> On Mon, Nov 15, 2010 at 08:01:20PM -0800, dirk.brandewie at gmail.com
>>>> wrote:
>>>>>
>>>>> From: Dirk Brandewie<dirk.brandewie at gmail.com>
>>>>>
>>>>> This patch adds support for linking device tree blobs into
>>>>> vmlinux. The device tree blobs are placed in the init.data
>>>>> section.
>>>>>
>>>>> Signed-off-by: Dirk Brandewie<dirk.brandewie at gmail.com>
>>>>> ---
>>>>>  include/asm-generic/vmlinux.lds.h |   19 +++++++++++++++++--
>>>>>  scripts/Makefile.lib              |   17 +++++++++++++++++
>>>>>  2 files changed, 34 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/include/asm-generic/vmlinux.lds.h
>>>>> b/include/asm-generic/vmlinux.lds.h
>>>>> index bd69d79..ea671e7 100644
>>>>> --- a/include/asm-generic/vmlinux.lds.h
>>>>> +++ b/include/asm-generic/vmlinux.lds.h
>>>>> @@ -67,7 +67,14 @@
>>>>>   * Align to a 32 byte boundary equal to the
>>>>>   * alignment gcc 4.5 uses for a struct
>>>>>   */
>>>>> -#define STRUCT_ALIGN() . = ALIGN(32)
>>>>> +#define STRUCT_ALIGNMENT 32
>>>>> +#define STRUCT_ALIGN() . = ALIGN(STRUCT_ALIGNMENT)
>>>>> +
>>>>> +/* Device tree blobs linked into the kernel need to have proper
>>>>> + * structure alignment to be parsed by the flat device tree library
>>>>> + * used in early boot
>>>>> +*/
>>>>> +#define DTB_ALIGNMENT STRUCT_ALIGNMENT
>>>>>
>>>>>  /* The actual configuration determine if the init/exit sections
>>>>>   * are handled as text/data or they can be discarded (which
>>>>> @@ -146,6 +153,13 @@
>>>>>  #define TRACE_SYSCALLS()
>>>>>  #endif
>>>>>
>>>>> +
>>>>> +#define KERNEL_DTB()
>>>>> \
>>>>> +       . = ALIGN(DTB_ALIGNMENT);
>>>>> \
>>>>> +       VMLINUX_SYMBOL(__dtb_start) = .;
>>>>>  \
>>>>> +       *(.dtb.init.rodata)
>>>>> \
>>>>> +       VMLINUX_SYMBOL(__dtb_end) = .;
>>>>> +
>>>>>  /* .data section */
>>>>>  #define DATA_DATA
>>>>> \
>>>>>        *(.data)
>>>>>  \
>>>>> @@ -468,7 +482,8 @@
>>>>>        MCOUNT_REC()
>>>>>  \
>>>>>        DEV_DISCARD(init.rodata)
>>>>>  \
>>>>>        CPU_DISCARD(init.rodata)
>>>>>  \
>>>>> -       MEM_DISCARD(init.rodata)
>>>>> +       MEM_DISCARD(init.rodata)
>>>>>  \
>>>>> +       KERNEL_DTB()
>>>>>
>>>>>  #define INIT_TEXT
>>>>> \
>>>>>        *(.init.text)
>>>>> \
>>>>> diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
>>>>> index 4c72c11..a8a4774 100644
>>>>> --- a/scripts/Makefile.lib
>>>>> +++ b/scripts/Makefile.lib
>>>>> @@ -200,6 +200,23 @@ quiet_cmd_gzip = GZIP    $@
>>>>>  cmd_gzip = (cat $(filter-out FORCE,$^) | gzip -f -9>    $@) || \
>>>>>        (rm -f $@ ; false)
>>>>>
>>>>> +# DTC
>>>>> +#
>>>>>
>>>>>  ---------------------------------------------------------------------------
>>>>> +$(obj)/%.dtb.S: $(obj)/%.dtb FORCE
>>>>> +       @echo '#include<asm-generic/vmlinux.lds.h>'>    $@
>>>>> +       @echo '.section .dtb.init.rodata,"a"'>>    $@
>>>>> +       @echo '.balign DTB_ALIGNMENT'>>    $@
>>>>> +       @echo '.global __dtb_$(*F)_begin'>>    $@
>>>>> +       @echo '__dtb_$(*F)_begin:'>>    $@
>>>>> +       @echo '.incbin "$<" '>>    $@
>>>>> +       @echo '__dtb_$(*F)_end:'>>    $@
>>>>> +       @echo '.global __dtb_$(*F)_end'>>    $@
>>>>> +       @echo '.balign DTB_ALIGNMENT'>>    $@
>>>>> +
>>>>> +DTC = $(objtree)/scripts/dtc/dtc
>>>>> +
>>>>> +quiet_cmd_dtc = DTC    $@
>>>>> +      cmd_dtc = $(DTC) -O dtb -o $(obj)/$*.dtb -b 0  $(src)/$*.dts
>>>>
>>>> Missing the %.dtb: %.dts rule, but otherwise looks okay.  You will
>>>> need to make sure this doesn't break powerpc or microblaze when the
>>>> dts->dtb rule is added.
>>>>
>>> I have the rule
>>>  $(obj)/%.dtb: $(src)/%.dts
>>>          $(call if_changed,dtc)
>>> in the arch/x86/kernel/Makefile to prevent this sneaking into other other
>>> architectures.
>>
>> This rule looks correct.  PowerPC and Microblaze need to be modified
>> to use it.  It should not be hard to do, give it a try.  Worst case,
>> your first attempt is wrong and the rest of us fix it up.  :-)
>>
>> Hint: PowerPC currently puts the .dtb file in a different directory
>> from the source .dts file.  It doesn't need to do it that way.
>> arch/powerpc/boot/Makefile will need to be modified.
>>
>
> I will give it a shot.  The only real difference except for the directory
> structures is powerpc and microblaze add padding to the dtb with the -p 1024
> command line argument to dtc.

You could use a $(DTCFLAGS) variable to pass in arch specific flags.

>  Is the padding needed when the blob are
> linked into vmlinux proper?

Maybe, maybe not.  Padding is required to be able to modify the .dtb
data in-place, which is important when adapting data from other
sources into the device tree structure.  However, when it is linked
into the kernel, the adding of additional data /possibly/ can be
deferred until after the tree is either copied or unflattened.

g.