[PATCH v4] fdt: Allow the devicetree to come from a bloblist

[Tom Rini]

On Wed, Dec 27, 2023 at 05:48:44PM +0000, Simon Glass wrote:
> Hi Ilias,
> 
> On Wed, Dec 27, 2023 at 6:44 AM Ilias Apalodimas
> <ilias.apalodimas at linaro.org> wrote:
> >
> > Hi Tom,
> >
> > On Tue, 26 Dec 2023 at 14:07, Tom Rini <trini at konsulko.com> wrote:
> > >
> > > On Tue, Dec 26, 2023 at 09:46:25AM +0000, Simon Glass wrote:
> > >
> > > > Standard passage provides for a bloblist to be passed from one firmware
> > > > phase to the next. That can be used to pass the devicetree along as well.
> > > > Add an option to support this.
> > > >
> > > > Tests for this will be added as part of the Universal Payload work.
> > > >
> > > > Signed-off-by: Simon Glass <sjg at chromium.org>
> > > > ---
> > > > The discussion on this was not resolved and is now important due to the
> > > > bloblist series from Raymond. So I am sending it again since I believe
> > > > this is a better starting point than building on OF_BOARD
> > >
> > > I really don't like adding another option for "DT is given to us". Why
> > > isn't adding another enum to fdt_source_t sufficient, and if we have
> > > bloblist enabled, that will look for and use if found? Maybe some other
> > > code needs to be restructured and cleaned up too?
> >
> > Same here. On top of that the bloblist has a few items in there, e.g a
> > TPM eventlog. What are we going to do? Add a Kconfig for each item?
> 
> No, but that is just a straw man. The DT is special and U-Boot reports
> where it comes from.
> 
> >
> > This has been going back and forth for a while. I've lost count of how
> > many times I repeated the same proposal, but here it goes again. We
> > have OF_BOARD and BLOBLIST options. The bloblist and its properties
> > are scannable at runtime. Can't we use the combination of these 2 can
> > be used to imply we expect things from a bloblist. If we want to be
> > stricter in the future and explicitly expect the DT from a bloblist,
> > we could add a Kconfig option failing the boot if that's missing.
> 
> I would like to have that Kconfig option now, not later. In my mind,
> the boot must be deterministic, so that if OF_BLOBLIST is enabled, the
> DT must come from there, or it is an error.

Determinism doesn't require a CONFIG option, it just requires an if/else
tree where we say what the "correct" priority list should be and then
set a flag so that we can tell the user where we found it too. This also
means that we can get whatever is going to use this mechanism to
migrate over, and have less of a chicken-and-egg type of problem.

> Also, repeating it doesn't make the proposal good. We agreed that
> OF_BOARD would eventually go away, so building on top of it is not
> setting us up for the future.

I wonder if OF_BOARD will ever go away, and I'm not convinced it will
either. Unless you just mean re-naming it and making a few ad-hoc
standards more easily re-usable, which also will need to happen
regardless.

-- 
Tom
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