Re: [PATCH v4 0/5] Add fastboot to SPL

On Fri Aug 21, 2026 at 2:21 PM CEST, Stefan Monnier wrote:
> Carlo Caione [2026-08-21 09:05:37] wrote:
>> It is possible to include U-Boot proper in the host-loaded bootstrap
>> and use its existing fastboot implementation. That is a valid approach
>> and is preferable where the Boot ROM download limit and memory budget
>> allow it.
>
> Right, that's the situation I'm familiar with.
>
>> But it is not always possible: some platforms (like the one we are
>> enabling) impose a strict size limit on the bootstrap, or only provide
>> enough early memory for the DDR initialization code and (small)
>> SPL-sized payload.
>
> I associate "fastboot" with the Android nebula, so I find it hard to
> imagine a machine with enough resources to run Android yet with a small
> enough boot memory for U-Boot not to fit into it.  I assume the SPL is
> pre-installed in some dedicated boot memory (SPI NOR?) whereas the main
> storage is left uninitialized during production.  And the NOR flash is
> so small that it can't even accommodate a proper U-Boot?
>
> I wonder how many cents it saves the manufacturer (e.g. compared to
> having a slightly bigger NOR, or not having the NOR at all and
> pre-installing U-Boot on the main storage) 🙁

Hi Stefan,

Just one clarification: SPL is not pre-installed in NOR here. The
Boot ROM downloads a transient bootstrap over USB into a fixed-size
on-chip memory window. That downloaded bootstrap then contains the DDR
initialization code and SPL, while the eMMC may be completely blank.

Also fastboot is used only as the provisioning protocol; it does not
imply Android.

For more info about the SPL on this kind of platforms you can also look
at [0], there is some documentation about this in there.

> Anyway, this is clearly getting offtopic.  Thanks for the answer.

Thanks for the discussion :)

Cheers,

[0] https://lore.kernel.org/all/20260814-ccaione-upstream-mt8390-spl-v4-0-f4f92978a79e@baylibre.com/

--
Carlo Caione