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

Mon Sep 25 07:53:59 PDT 2023

Hi Miquel,

On Mon, 25 Sept 2023 at 08:47, Miquel Raynal <miquel.raynal at bootlin.com> wrote:
>
> Hi Simon,
>
> sjg at chromium.org wrote on Mon, 25 Sep 2023 06:33:14 -0600:
>
> > Hi Miquel,
> >
> > On Mon, 25 Sept 2023 at 01:21, Miquel Raynal <miquel.raynal at bootlin.com> wrote:
> > >
> > > Hi Simon,
> > >
> > > sjg at chromium.org wrote on Fri, 22 Sep 2023 13:51:14 -0600:
> > >
> > > > Hi Rob,
> > > >
> > > > On Fri, 22 Sept 2023 at 13:43, Rob Herring <robh at kernel.org> wrote:
> > > > >
> > > > > On Fri, Sep 22, 2023 at 1:12 PM Simon Glass <sjg at chromium.org> wrote:
> > > > > >
> > > > > > Hi Rob,
> > > > > >
> > > > > > On Fri, 22 Sept 2023 at 11:46, Rob Herring <robh at kernel.org> wrote:
> > > > > > >
> > > > > > > On Fri, Sep 22, 2023 at 11:01:18AM -0600, Simon Glass wrote:
> > > > > > > > Hi Rob,
> > > > > > > >
> > > > > > > > On Fri, 22 Sept 2023 at 10:00, Rob Herring <robh at kernel.org> wrote:
> > > > > > > > >
> > > > > > > > > On Thu, Sep 21, 2023 at 1:45 PM Simon Glass <sjg at chromium.org> wrote:
> > > > > > > > > >
> > > > > > > > > > Binman[1] is a tool for creating firmware images. It allows you to
> > > > > > > > > > combine various binaries and place them in an output file.
> > > > > > > > > >
> > > > > > > > > > Binman uses a DT schema to describe an image, in enough detail that
> > > > > > > > > > it can be automatically built from component parts, disassembled,
> > > > > > > > > > replaced, listed, etc.
> > > > > > > > > >
> > > > > > > > > > Images are typically stored in flash, which is why this binding is
> > > > > > > > > > targeted at mtd. Previous discussion is at [2] [3].
> > > > > > > > > >
> > > > > > > > > > [1] https://u-boot.readthedocs.io/en/stable/develop/package/binman.html
> > > > > > > > > > [2] https://lore.kernel.org/u-boot/20230821180220.2724080-3-sjg@chromium.org/
> > > > > > > > > > [3] https://www.spinics.net/lists/devicetree/msg626149.html
> > > > > > > > >
> > > > > > > > > You missed:
> > > > > > > > >
> > > > > > > > > https://github.com/devicetree-org/dt-schema/pull/110
> > > > > > > > >
> > > > > > > > > where I said: We certainly shouldn't duplicate the existing partitions
> > > > > > > > > bindings. What's missing from them (I assume we're mostly talking
> > > > > > > > > about "fixed-partitions" which has been around forever I think (before
> > > > > > > > > me))?
> > > > > > > > >
> > > > > > > > > To repeat, unless there is some reason binman partitions conflict with
> > > > > > > > > fixed-partitions, you need to start there and extend it. >From what's
> > > > > > > > > posted here, it neither conflicts nor needs extending.
> > > > > > > >
> > > > > > > > I think at this point I am just hopelessly confused. Have you taken a
> > > > > > > > look at the binman schema? [1]
> > > > > > >
> > > > > > > Why do I need to? That's used for some tool and has nothing to do with a
> > > > > > > device's DTB. However, I thought somewhere in this discussion you showed
> > > > > > > it under a flash device node.
> > > > > >
> > > > > > Yes, that is the intent (under a flash node).
> > > > > >
> > > > > > > Then I care because then it overlaps with
> > > > > > > what we already have for partitions. If I misunderstood that, then just
> > > > > > > put your schema with your tool. Only users of the tool should care about
> > > > > > > the tool's schema.
> > > > > >
> > > > > > OK. I believe that binman will fit into both camps, since its input is
> > > > > > not necessarily fully formed. E.g. if you don't specify the offset of
> > > > > > an entry, then it will be packed automatically. But the output is
> > > > > > fully formed, in that Binman now knows the offset so can write it to
> > > > > > the DT.
> > > > >
> > > > > I suppose it could take its own format as input and then write out
> > > > > something different for the "on the device" format (i.e.
> > > > > fixed-partitions). At least for the dynamic offsets, we may need
> > > > > something allowed for binman input, but not allowed on device. In
> > > > > general, there is support for partitions without addresses/offsets,
> > > > > but only for partitions that have some other way to figure that out
> > > > > (on disk partition info).
> > > > >
> > > > > There's also the image filename which doesn't really belong in the on
> > > > > device partitions. So maybe the input and output schemas should be
> > > > > separate.
> > > >
> > > > OK, I'll focus on the output schema for now. I suspect this will be a
> > > > grey area though.
> > > >
> > > > As an example, if you replace a binary in the firmware, Binman can
> > > > repack the firmware to make room, respecting the alignment and size
> > > > constraints. So these need to be in the output schema somehow.
> > > >
> > > > >
> > > > > > > > I saw this file, which seems to extend a partition.
> > > > > > > >
> > > > > > > > Documentation/devicetree/bindings/mtd/partitions/brcm,bcm4908-partitions.yaml
> > > > > > >
> > > > > > > IIRC, that's a different type where partition locations are stored in
> > > > > > > the flash, so we don't need location and size in DT.
> > > > > >
> > > > > > OK.
> > > > > >
> > > > > > >
> > > > > > > >
> > > > > > > > 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".

What mechanism do you suggest be used here?

>
> > > > > We already have some compatibles in use. We should reuse them if
> > > > > possible. Not sure about TF-A though.
> > > >
> > > > OK.
> > > >
> > >
> > > 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. 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.

>
> > [1] https://u-boot.readthedocs.io/en/latest/develop/package/index.html
> > [2] https://pretalx.com/media/osfc2019/submissions/Y7EN9V/resources/Binman_-_A_data-controlled_firmware_packer_for_U-B_pFU3n2K.pdf
> > [3] https://www.youtube.com/watch?v=L84ujgUXBOQ
>

Regards,
Simon