[PATCH] dt-bindings: mtd: Add a schema for binman

[Simon Glass]

Hi Rob,

On Mon, 25 Sept 2023 at 12:49, Rob Herring <robh at kernel.org> wrote:
>
> On Mon, Sep 25, 2023 at 11:25 AM Simon Glass <sjg at chromium.org> wrote:
> >
> > Hi Miquel,
> >
> > On Mon, 25 Sept 2023 at 09:24, Miquel Raynal <miquel.raynal at bootlin.com> wrote:
> > >
> > > Hi Simon,
> > >
> > > > > > > > > > > > I was assuming that I should create a top-level compatible = "binman"
> > > > > > > > > > > > node, with subnodes like compatible = "binman,bl31-atf", for example.
> > > > > > > > > > > > I should use the compatible string to indicate the contents, right?
> > > > > > > > > > >
> > > > > > > > > > > Yes for subnodes, and we already have some somewhat standard ones for
> > > > > > > > > > > "u-boot" and "u-boot-env". Though historically, "label" was used.
> > > > > > > > > >
> > > > > > > > > > Binman has common properties for all entries, including "compress"
> > > > > > > > > > which sets the compression algorithm.
> > > > > > > > >
> > > > > > > > > I see no issue with adding that. It seems useful and something missing
> > > > > > > > > in the existing partition schemas.
> > > > > > > >
> > > > > > > > OK I sent a patch with that.
> > > > > > > >
> > > > > > > > >
> > > > > > > > > > So perhaps I should start by defining a new binman,bl31-atf which has
> > > > > > > > > > common properties from an "binman,entry" definition?
> > > > > > > > >
> > > > > > > > > I don't understand the binman prefix. The contents are ATF (or TF-A
> > > > > > > > > now). Who wrote it to the flash image is not relevant.
> > > > > > > >
> > > > > > > > Are you suggesting just "atf-bl31", or "arm,atf-bl31" ? Or should we
> > > > > > > > change it to "tfa-bl31"?
> > > > > > >
> > > > > > > I don't really understand the relationship with TF-A here. Can't we
> > > > > > > just have a kind of fixed-partitions with additional properties like
> > > > > > > the compression?
> > > > > >
> > > > > > Binman needs to know what to put in there, which is the purpose of the
> > > > > > compatible string.
> > > > >
> > > > > But "what" should be put inside the partition is part of the input
> > > > > argument, not the output. You said (maybe I got this wrong) that the
> > > > > schema would apply to the output of binman. If you want to let user
> > > > > know what's inside, maybe it is worth adding a label, but otherwise I
> > > > > don't like the idea of a compatible for that, which for me would mean:
> > > > > "here is how to handle that specific portion of the flash/here is how
> > > > > the flash is organized".
> > > >
> > > > But I thought that the compatible string was for that purpose? See for
> > > > example "brcm,bcm4908-firmware" and "brcm,bcm963xx-imagetag" and
> > > > "linksys,ns-firmware".
> > >
> > > These three examples apparently need specific handling, the partitions
> > > contain meta-data that a parser needs to check or something like that.
> > > And finally it looks like partition names are set depending on the
> > > content that was discovered, so yes, the partition name is likely the
> > > good location to tell users/OSes what's inside.
> > >
> > > > > > > Also, I still don't understand the purpose of this schema. So binman
> > > > > > > generates an image, you want to flash this image and you would like the
> > > > > > > tool to generate the corresponding (partition) DT snippet automatically.
> > > > > > > Do I get this right? I don't get why you would need new compatibles for
> > > > > > > that.
> > > > > >
> > > > > > It is actually the other way around. The schema tells Binman how to
> > > > > > build the image (what goes in there and where). Then outputs an
> > > > > > updated DT which describes where everything ended up, for use by other
> > > > > > tools, e.g. firmware update. It is a closed loop in that sense. See
> > > > > > the references for more information.
> > > > >
> > > > > Maybe I fail to see why you would want these description to be
> > > > > introduced here, if they are not useful to the OS.
> > > >
> > > > Well I was asked to send them to Linux since they apparently don't
> > > > belong in dt-schema.
>
> That is not what I said. I said fixed-partitions should be extended. I
> prefer they are extended in-place before moving them rather than the
> other way around.

OK.

>
> > > > These are firmware bindings, as indicated, but I
> > > > took them out of the /firmware node since that is for a different
> > > > purpose. Rob suggested that partitions was a good place. We have fwupd
> > > > using DT to hold the firmware-update information, so I expect it will
> > > > move to use these bindings too.
> > >
> > > I would definitely use fixed partitions as that's what you need then:
> > > registering where everything starts and ends. If you have "in-band"
> > > meta data you might require a compatible, but I don't think you
> > > do, in this case you should probably carry the content through a label
> > > (which will become the partition name) and we can discuss additional
> > > properties if needed.
> >
> > I believe I am going to need a compatible string at the 'partitions'
> > level to indicate that this is the binman scheme. But we can leave
> > that until later.
>
> Perhaps:
>
> compatible = "binman", "fixed-partitions";
>
> Though I don't understand why binman couldn't just understand what
> "fixed-partitions" means rather than "binman".

Well so long as we don't add any binman things in here, you are right.

But the eventual goal is parity with current Binman functionality,
which writes the entire (augmented) description to the DT, allowing
tools to rebuild / repack / replace pieces later, maintaining the same
alignment constraints, etc. I am assuming that properties like 'align
= <16>' would not fit with fixed-partitions. But if we don't preserve
these properties then Binman cannot do repacking reliably. Perhaps for
now I could put the augmented DT in its own section somewhere, but I
am just not sure if that will work in a real system. E.g. with VBE the
goal is to use the DT to figure out how to access the firmware, update
it, etc.

Is it not possible to have my own node with whatever things Binman
needs in it (subject to review of course)? i.e. could we discuss how
to encode it, but argue less about whether things are needed? I
kind-of feel I know what is needed, since I wrote the tool.

>
>
> > So you are suggesting 'label' for the contents. Rob suggested
> > 'compatible' [1], so what should I do?
>
> "label" is for consumption by humans, not tools/software. Compatible
> values are documented, label values are not. Though the partition
> stuff started out using label long ago and it's evolved to preferring
> compatible.

OK so we are agreed that we are going with 'compatible'.

>
> > With this schema, would every node be called 'partition at ...' or is
> > there flexibility to use other names?
>
> The preference is to use generic names. Do you mean without a
> unit-address or different from "partition"? The need for the input
> side of binman to have dynamic addresses seems like the biggest issue.
> That's allowed in other cases with "partition-N" or "partition-foo"
> IIRC. I don't think we want to allow that for "fixed-partitions" at
> least in the DTB (i.e. the output side of binman).

OK I suppose this is the problem with starting small. I was hoping to
build up the schema piece by piece but now I am wondering whether
every little detail will get redirected and I'll end up with something
that Binman cannot use.

So far all I have is that I can add a 'compress' property and a
'compatible' which describes the contents. I suppose it is a start.

Regards,
Simon