Re: [PATCH v4 2/3] dt-bindings: mtd: binman-partition: Add binman compatibles

[Miquel Raynal <miquel.raynal@bootlin.com>]

Hi Simon,

sjg@chromium.org wrote on Tue, 24 Oct 2023 14:40:54 -0700:

> Hi Rob,
> 
> On Tue, 24 Oct 2023 at 09:16, Rob Herring <robh@kernel.org> wrote:
> >
> > On Mon, Oct 09, 2023 at 04:04:14PM -0600, Simon Glass wrote:  
> > > Add two compatible for binman entries, as a starting point for the
> > > schema.
> > >
> > > Note that, after discussion on v2, we decided to keep the existing
> > > meaning of label so as not to require changes to existing userspace
> > > software when moving to use binman nodes to specify the firmware
> > > layout.
> > >
> > > Signed-off-by: Simon Glass <sjg@chromium.org>
> > > ---
> > >
> > > Changes in v4:
> > > - Correct selection of multiple compatible strings
> > >
> > > Changes in v3:
> > > - Drop fixed-partitions from the example
> > > - Use compatible instead of label
> > >
> > > Changes in v2:
> > > - Use plain partition@xxx for the node name
> > >
> > >  .../mtd/partitions/binman-partition.yaml      | 49 +++++++++++++++++++
> > >  1 file changed, 49 insertions(+)
> > >  create mode 100644 Documentation/devicetree/bindings/mtd/partitions/binman-partition.yaml
> > >
> > > diff --git a/Documentation/devicetree/bindings/mtd/partitions/binman-partition.yaml b/Documentation/devicetree/bindings/mtd/partitions/binman-partition.yaml
> > > new file mode 100644
> > > index 000000000000..35a320359ec1
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/mtd/partitions/binman-partition.yaml
> > > @@ -0,0 +1,49 @@
> > > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> > > +# Copyright 2023 Google LLC
> > > +
> > > +%YAML 1.2
> > > +---
> > > +$id: http://devicetree.org/schemas/mtd/partitions/binman-partition.yaml#
> > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > +
> > > +title: Binman partition
> > > +
> > > +maintainers:
> > > +  - Simon Glass <sjg@chromium.org>
> > > +
> > > +select: false  
> >
> > So this schema is never used. 'select: false' is only useful if
> > something else if referencing the schema.  
> 
> OK. Is there a user guide to this somewhere? I really don't understand
> it very well.

The example-schema.yaml at the root of the dt-bindings directory is
well commented.

> > > +description: |
> > > +  This corresponds to a binman 'entry'. It is a single partition which holds
> > > +  data of a defined type.
> > > +
> > > +allOf:
> > > +  - $ref: /schemas/mtd/partitions/partition.yaml#
> > > +
> > > +properties:
> > > +  compatible:
> > > +    oneOf:
> > > +      - const: binman,entry     # generic binman entry  
> >
> > 'binman' is not a vendor. You could add it if you think that's useful.
> > Probably not with only 1 case...  
> 
> I think it is best to use this for generic things implemented by
> binman, rather than some other project. For example, binman supports a
> 'fill' region. It also supports sections which are groups of
> sub-entries. So we will likely start with half a dozen of these and it
> will likely grow: binman,fill, binman,section, binman,files
> 
> If we don't use 'binman', what do you suggest?
> 
> >  
> > > +      - items:
> > > +          - const: u-boot       # u-boot.bin from U-Boot project
> > > +          - const: atf-bl31     # bl31.bin or bl31.elf from TF-A project  
> >
> > Probably should use the new 'tfa' rather than old 'atf'. Is this the
> > only binary for TFA? The naming seems inconsistent in that every image
> > goes in (or can go in) a bl?? section. Why does TFA have it but u-boot
> > doesn't? Perhaps BL?? is orthogonal to defining what is in each
> > partition. Perhaps someone more familar with all this than I am can
> > comment.  
> 
> From what I can tell TF-A can produce all sorts of binaries, of which
> bl31 is one. U-Boot can also produce lots of binaries, but its naming
> is different (u-boot, u-boot-spl, etc.). Bear in mind that U-Boot is
> used on ARM, where this terminology is defined, and on x86 (for
> example), where it is not.
> 
> >
> > Once you actually test this, you'll find you are specifying:
> >
> > compatible = "u-boot", "atf-bl31";  
> 
> I don't understand that, sorry. I'll send a v5 and see if the problem goes away.

For me this means the partition contains U-Boot and TF-A, which is
probably not what you want. I believe Rob is saying that how you define
the compatible property above does not match the examples below. Did
you run make dt_binding_check?

Also, do you really need to say which software project provides a
component? Would using "bl31", "bl33", etc be enough? Or maybe you
could have eg. "bl31-tf-a" and "bl31-u-boot-spl" (in this order) for
clarity? This way one knows which stage a partition contains and also
the software project which provided it.

To be honest I still don't fully get where you want to go and I believe
a more complete schema would probably help, with different examples, to
catch what you need and why.

> > > +additionalProperties: false
> > > +
> > > +examples:
> > > +  - |
> > > +    partitions {
> > > +        compatible = "binman";
> > > +        #address-cells = <1>;
> > > +        #size-cells = <1>;
> > > +
> > > +        partition@100000 {
> > > +            compatible = "u-boot";
> > > +            reg = <0x100000 0xf00000>;
> > > +        };
> > > +
> > > +        partition@200000 {
> > > +            compatible = "atf-bl31";
> > > +            reg = <0x200000 0x100000>;
> > > +        };
> > > +    };
> > > --
> > > 2.42.0.609.gbb76f46606-goog
> > >  
> 
> Regards,
> Simon


Thanks,
Miquèl