Re: [PATCH 2/3] dt-bindings: mtd: Add Documentation for Airoha fixed-partitions

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

Hi Christian,

ansuelsmth@gmail.com wrote on Wed, 25 Sep 2024 13:35:38 +0200:

> On Wed, Sep 25, 2024 at 01:30:03PM +0200, Miquel Raynal wrote:
> > Hi Christian,
> > 
> > ansuelsmth@gmail.com wrote on Wed, 25 Sep 2024 12:13:58 +0200:
> >   
> > > Add Documentation for Airoha fixed-partitions compatibles.
> > > 
> > > Airoha based SoC declare a dedicated partition at the end of the flash to
> > > store calibration and device specific data, in addition to fixed
> > > partitions.
> > > 
> > > The offset of this special partition is not well defined as a custom bad
> > > block management driver is used that reserve space at the end of the flash.
> > > 
> > > This binding allows defining all fixed partitions and marking the last one
> > > to detect the correct offset.
> > > 
> > > Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
> > > ---
> > >  .../partitions/airoha,fixed-partitions.yaml   | 80 +++++++++++++++++++
> > >  .../bindings/mtd/partitions/partitions.yaml   |  1 +
> > >  2 files changed, 81 insertions(+)
> > >  create mode 100644 Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml
> > > 
> > > diff --git a/Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml b/Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml
> > > new file mode 100644
> > > index 000000000000..a45df51065af
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/mtd/partitions/airoha,fixed-partitions.yaml
> > > @@ -0,0 +1,80 @@
> > > +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
> > > +%YAML 1.2
> > > +---
> > > +$id: http://devicetree.org/schemas/mtd/partitions/airoha,fixed-partitions.yaml#
> > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > +
> > > +title: Airoha SoC partitioning
> > > +
> > > +description: |
> > > +  Airoha based SoC declare a dedicated partition at the end of the flash to
> > > +  store calibration and device specific data, in addition to fixed partitions.
> > > +
> > > +  The offset of this special partition is not well defined as a custom bad block
> > > +  management driver is used that reserve space at the end of the flash.
> > > +
> > > +  This binding allows defining all fixed partitions and marking the last one to
> > > +  detect the correct offset from the new end of the flash.
> > > +
> > > +maintainers:
> > > +  - Christian Marangi <ansuelsmth@gmail.com>
> > > +
> > > +select: false
> > > +
> > > +properties:
> > > +  compatible:
> > > +    const: airoha,fixed-partitions
> > > +
> > > +  "#address-cells":
> > > +    enum: [ 1, 2 ]
> > > +
> > > +  "#size-cells":
> > > +    enum: [ 1, 2 ]
> > > +
> > > +patternProperties:
> > > +  "^partition@[0-9a-f]+$":
> > > +    $ref: partition.yaml#
> > > +    properties:
> > > +      compatible:
> > > +        const: airoha,dynamic-art
> > > +    unevaluatedProperties: false
> > > +
> > > +required:
> > > +  - "#address-cells"
> > > +  - "#size-cells"
> > > +
> > > +additionalProperties: false
> > > +
> > > +examples:
> > > +  - |
> > > +    partitions {
> > > +        compatible = "airoha,fixed-partitions";
> > > +        #address-cells = <1>;
> > > +        #size-cells = <1>;
> > > +
> > > +        partition@0 {
> > > +          label = "bootloader";
> > > +          reg = <0x00000000 0x00080000>;
> > > +        };
> > > +
> > > +        partition@80000 {
> > > +          label = "tclinux";
> > > +          reg = <0x00080000 0x02800000>;
> > > +        };
> > > +
> > > +        partition@2880000 {
> > > +          label = "tclinux_slave";
> > > +          reg = <0x02880000 0x02800000>;
> > > +        };
> > > +
> > > +        partition@5080000 {
> > > +          label = "rootfs_data";
> > > +          reg = <0x5080000 0x00800000>;
> > > +        };
> > > +
> > > +        partition@ffffffff {
> > > +          compatible = "airoha,dynamic-art";
> > > +          label = "art";
> > > +          reg = <0xffffffff 0x00300000>;  
> > 
> > I'm a little bit puzzled by this kind of information which is known to
> > be wrong. As the partition offset and size must be dynamically
> > calculated, this reg property (as well as the size parameter of the
> > previous one) are notably wrong. I guess we are not fully constrained
> > by the fixed-partitions schema here, so could we avoid the reg property
> > in the airoha,dynamic-art partition? Maybe we also need a #define for a
> > specific placeholder in the penultimate reg property too (for the size).
> >  
> 
> Maybe instead of reg we can use a property like size?
> 
> Can you better elaborate the suggestion about the #define?
> 
> Do you mean for case where the last partition might overlap
> with the penultimate? Honestly in such case I would error hard, that
> case happen when too much space is reserved and that is a
> misconfiguration of the system (developer error)

That's not what I mean.

In the above case you say partition "partition@5080000" is 0x800000
bytes long. This is obviously wrong otherwise you would know where the
art partition starts. And right after you're saying partition
"partition@ffffffff" starts at 0xffffffff and is 0x300000 bytes long.
This is also wrong because 0xffffffff is not a valid start address and
IIUC 0x300000 is also unknown and dynamically derived.

So for the art partition my advise if you know nothing about the
start/length is to just skip the reg property. For the previous
partition I'd maybe use a definition (whose name is to discuss) instead
of the wrong size argument (the start offset being correct on his side).

Thanks, Miquèl