One barebox image for multiple boards

[Sascha Hauer]

On Fri, May 13, 2022 at 02:10:32PM +0200, Matthias Fend wrote:
> Hi Sascha,
> 
> Am 13.05.2022 um 13:00 schrieb Sascha Hauer:
> > Hi Matthias,
> > 
> > On Fri, May 13, 2022 at 10:55:02AM +0200, Matthias Fend wrote:
> > > Hi,
> > > 
> > > I'm looking for a solution to support multiple boards with just one barebox
> > > image. The few core components that are relevant for barebox are the same on
> > > all boards, so that the same barebox image runs on all boards. It is
> > > possible to dynamically detect the board type inside barebox, but as this
> > > requires some infrastructure it is not possible during lowlevel init. So
> > > basically Barebox should boot with a minimal core device tree, detect the
> > > board type and then use the corresponding device tree of the detected board.
> > > Something similar to arch/arm/boards/stm32mp15xx-dkx/lowlevel.c but not at
> > > low level.
> > 
> > Do you even need the full device tree in barebox? The minimal core
> > device tree might be enough for barebox and only the kernel is then
> > booted with the full device tree.
> 
> If there is no trick to changing the used device tree at boardlevel init,
> then this might be a possibility.

Replacing the live tree after it has been partly probed already is
dangerous and barebox is not really prepared for that.

> The core device tree might not be as minimal then and in exceptional cases
> minor fixups in the board code will be needed, but I think it could work.
> 
> In such a case, how should one ensure that the appropriate blspec entry is
> booted? Maybe by simply replacing/updating the compatible string in the live
> device tree after the board was detected?

As it happens Oleksij has just introduced of_prepend_machine_compatible()
exactly for this usecase. You can find it in current next branch.

Sascha

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