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-f4f92978a...@baylibre.com/ -- Carlo Caione
