[PATCH v2 1/2] scripts/Makefile.xpl: Align filtered DTB to 8-byte within multidtb.fit

[Marek Vasut]

On 1/13/26 4:00 PM, Tom Rini wrote:
> On Tue, Jan 13, 2026 at 12:53:39AM +0100, Marek Vasut wrote:
>> On 1/12/26 11:03 PM, Tom Rini wrote:
>>
>>>>> This we can fix in the Makefile via the dd command as suggested by Tom.
>>>>
>>>> My concern is about LEGACY fitImages (means already generated ones), not
>>>> newly generated ones.
>>>
>>> Why is that a concern? If it's a legacy fitImage for the OS, we relocate
>>> the device tree already normally to be aligned. If it's a legacy
>>> fitImage of U-Boot, it's an old U-Boot?
>>
>> Not necessarily, it could be new U-Boot using old fitImage, for whatever
>> reason (falcon boot maybe ?). We should not break that.
> 
> If it's falcon boot then it's the OS case and we relocate it before
> passing on, that's not changed.

Not always, cf the whole fdt_high=-1 bag of issues.

What I would like to see is something like

8fbcc0e0e839 ("boot: Assure FDT is always at 8-byte aligned address")

then we are safe against all obscure 4-byte-alignment cases.

> That's why I'm saying I'm not sure
> there's a legacy case to worry about, since the big change now is that
> U-Boot also demands correctly aligned device trees. The Linux Kernel
> essentially always has, and other OSes probably as well. We were just
> bad and let 4-byte work for so long.
> 
>>>>>> - Should mkimage -E align blobs to 8 bytes by default ? I think yes,
>>>>>> and frankly, I thought it does so already, but apparently not.
>>>>>
>>>>>
>>>>> This can be done, but should it be? Not all FITs demand an 8-byte
>>>>> alignment right? It is only the FDT which requires this.
>>>> Maybe if image type is flat_dt, it should be implicitly 8-byte aligned then
>>>> ?
>>>
>>> Well, the device tree spec says 8-byte alignment.
>>
>> 8 byte alignment of what, start of DT, right ?
>>
>>> It's not "FDT for OS"
>>> that's 8-byte, it's any device tree should start out 8 byte aligned, and
>>> everything else should then be naturally aligned. If we're looking in a
>>> device tree for another device tree to use in place and not relocate
>>> then that second tree must be aligned.
>>>
>>> Or am I missing something?
>> The discussion is about mkimage -E which generates DTs for U-Boot SPL use.
>> The DTs in those external data should likely be aligned to 8 bytes by
>> default, i.e. implicitly set -B 8 (they don't seem to be right now).
> 
> Right. So the only legacy case I can see would be using an old mkimage
> to generate a current U-Boot image. And I'm not super sure that can
> happen, outside of some sort of external to us tooling being wrapped
> around things, and at that point we have little control.
For that case, see above.