linux-kernel - Re: [RFC PATCH 1/2] dt-bindings: mtd: partitions: Document new dynamic-partitions node

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Message-ID: <61eb5004.1c69fb81.43dc1.b0f4@mx.google.com>
Date:   Sat, 22 Jan 2022 01:29:54 +0100
From:   Ansuel Smith <ansuelsmth@...il.com>
To:     Rob Herring <robh@...nel.org>
Cc:     Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        linux-mtd@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/2] dt-bindings: mtd: partitions: Document new
 dynamic-partitions node

On Thu, Jan 20, 2022 at 07:49:26PM -0600, Rob Herring wrote:
> On Thu, Jan 20, 2022 at 09:26:14PM +0100, Ansuel Smith wrote:
> > Document new dynamic-partitions node used to provide an of node for
> > partition registred at runtime by parsers. This is required for nvmem
> > system to declare and detect nvmem-cells.
> 
> So you have some discoverable way to find all the partitions and the 
> nvmem cells are at an unknown (to the DT) location, but still need to be 
> described in DT?
>

Example: smem partition layout is saved in the bootloader and static. To
know the layout just boot the device and extract it. Aside from this the
naming convention is ""standard"" (example the standard nvmem location
for this is named 0:art)

What needs to be described in the DT is the cell offset and the
partition name (the location)

NVMEM doesn't support this and honestly I can't think of a simple and
direct way to solve this. Considering partition in this case are just
filled at runtime and they doesn't change (or at worst the partition
offset change but NEVER the name) it seems a good way to fix this by
describing a nvmem cells partition name and assign a of node to the
runtime filled partition.

> > Signed-off-by: Ansuel Smith <ansuelsmth@...il.com>
> > ---
> >  .../mtd/partitions/dynamic-partitions.yaml    | 59 +++++++++++++++++++
> >  1 file changed, 59 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/mtd/partitions/dynamic-partitions.yaml
> > 
> > diff --git a/Documentation/devicetree/bindings/mtd/partitions/dynamic-partitions.yaml b/Documentation/devicetree/bindings/mtd/partitions/dynamic-partitions.yaml
> > new file mode 100644
> > index 000000000000..7528e49f2d7e
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/mtd/partitions/dynamic-partitions.yaml
> > @@ -0,0 +1,59 @@
> > +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/mtd/partitions/dynamic-partitions.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Dynamic partitions
> > +
> > +description: |
> > +  This binding can be used on platforms which have partitions registered at
> > +  runtime by parsers or partition table present on the flash. Example are
> > +  partitions declared from smem parser or cmdlinepart. This will create an
> 
> Some information in DT and some on the cmdline seems broken to me. Pick 
> one or the other.
> 

Converting a system from cmdline to fixedpartition is problematic
if the cmdline is dynamic. Example some system have dual partition and
are handled by editing the cmdline partition description. In this
cmdline tho the nvmem cell of our interest doesn't change and we can use
this new implemenation to add support for nvmem cells.

So really there are some case where nvmem won't work and it's not
possible to provide a correct configuration for nvmem to work correctly.

Is it that bad to have information in the DT about nvmem cells for a
partition named with a particular label that won't change.

> > +  of node for these dynamic partition where systems like Nvmem can get a
> > +  reference to register nvmem-cells.
> > +
> > +  The partition table should be a node named "dynamic-partitions".
> > +  Partitions are then defined as subnodes. Only the label is required
> > +  as any other data will be taken from the parser.
> > +
> > +maintainers:
> > +  - Ansuel Smith <ansuelsmth@...il.com>
> > +
> > +properties:
> > +  compatible:
> > +    const: dynamic-partitions
> 
> This is useless. This tells me nothing about the what's in the 
> partitions.
> 
> > +
> > +patternProperties:
> > +  "@[0-9a-f]+$":
> > +    $ref: "partition.yaml#"
> > +
> > +additionalProperties: true
> > +
> > +examples:
> > +  - |
> > +    partitions {
> > +        compatible = "qcom,smem";
> > +        #address-cells = <1>;
> > +        #size-cells = <1>;
> > +    };
> > +
> > +    dynamic-partitions {
> > +      compatible = "dynamic-partitions";
> > +
> > +      art: art {
> > +        label = "0:art";
> > +        read-only;
> > +        compatible = "nvmem-cells";
> > +        #address-cells = <1>;
> > +        #size-cells = <1>;
> > +
> > +        macaddr_art_0: macaddr@0 {
> > +          reg = <0x0 0x6>;
> > +        };
> > +
> > +        macaddr_art_6: macaddr@6 {
> > +          reg = <0x6 0x6>;
> > +        };
> > +      };
> > +    };
> > -- 
> > 2.33.1
> > 
> > 

-- 
	Ansuel