Re: [RFC v2 1/3] dt-bindings: nvmem: Add devicetree bindings for qfprom-efuse

[Srinivas Kandagatla]

On 12/06/2020 22:59, Doug Anderson wrote:
> Hi,
>
> On Thu, Jun 11, 2020 at 2:49 AM Ravi Kumar Bokka <rbokka@xxxxxxxxxxxxxx> wrote:
> > This patch adds dt-bindings document for qfprom-efuse controller.
> >
> > Signed-off-by: Ravi Kumar Bokka <rbokka@xxxxxxxxxxxxxx>
> > ---
> >   .../devicetree/bindings/nvmem/qfprom.yaml          | 52 ++++++++++++++++++++++
> >   1 file changed, 52 insertions(+)
>
> Overall comment: I reviewed your v1 series and so I'm obviously
> interested in your series.  Please CC me on future versions.
>
> I would also note that, since this is relevant to Qualcomm SoCs that
> you probably should be CCing "linux-arm-msm@xxxxxxxxxxxxxxx" on your
> series.
>
>
> >   create mode 100644 Documentation/devicetree/bindings/nvmem/qfprom.yaml
> >
> > diff --git a/Documentation/devicetree/bindings/nvmem/qfprom.yaml b/Documentation/devicetree/bindings/nvmem/qfprom.yaml
> > new file mode 100644
> > index 0000000..7c8fc31
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/nvmem/qfprom.yaml
> > @@ -0,0 +1,52 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/nvmem/qfprom.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Qualcomm Technologies Inc, QFPROM Efuse bindings
> > +
> > +maintainers:
> > +  - Ravi Kumar Bokka <rbokka@xxxxxxxxxxxxxx>
> > +
> > +allOf:
> > +  - $ref: "nvmem.yaml#"
> > +
> > +properties:
> > +  compatible:
> > +    enum:
> > +      - qcom,qfprom
>
> As per discussion in patch #1, I believe SoC compatible should be here
> too in case it is ever needed.  This is standard practice for dts
> files for IP blocks embedded in an SoC.  AKA, this should be:
>
>      items:
>        - enum:
>            - qcom,apq8064-qfprom
>            - qcom,apq8084-qfprom
>            - qcom,msm8974-qfprom
>            - qcom,msm8916-qfprom
>            - qcom,msm8996-qfprom
>            - qcom,msm8998-qfprom
>            - qcom,qcs404-qfprom
>            - qcom,sc7180-qfprom
>            - qcom,sdm845-qfprom


Above is not required for now in this patchset, as we can attach data at 
runtime specific to version of the qfprom.

This can be added when required!

>        - const: qcom,qfprom
>
> NOTE: old SoCs won't have both of these and thus they will get flagged
> with "dtbs_check", but I believe that's fine (Rob can correct me if
> I'm wrong).  The code should still work OK if the SoC isn't there but
> it would be good to fix old dts files to have the SoC specific string
> too.
>
>
> > +
> > +  reg:
> > +    maxItems: 3
>
> Please address feedback feedback on v1.  If you disagree with my
> feedback it's OK to say so (I make no claims of being always right),
> but silently ignoring my feedback and sending the next version doesn't
> make me feel like it's a good use of my time to keep reviewing your
> series.  Specifically I suggested that you actually add descriptions
> rather than just putting "maxItems: 3".
>
> With all that has been discussed, I think the current best thing to
> put there is:
>
>      # If the QFPROM is read-only OS image then only the corrected region
>      # needs to be provided.  If the QFPROM is writable then all 3 regions
>      # must be provided.
>      oneOf:
>        - items:
>            - description: The start of the corrected region.
>        - items:
>            - description: The start of the raw region.
>            - description: The start of the config region.
>            - description: The start of the corrected region.
>
> > +
>
> You missed a bunch of things that you should document:
>
>    # Clocks must be provided if QFPROM is writable from the OS image.
>    clocks:
>      maxItems: 1
>    clock-names:
>      const: sec
>
>    # Supply reference must be provided if QFPROM is writable from the OS image.
>    vcc-supply:
>      description: Our power supply.
>
>    # Needed if any child nodes are present.
>    "#address-cells":
>      const: 1
>    "#size-cells":
>      const: 1
>
> > +required:
> > +   - compatible
> > +   - reg
> > +   - reg-names
>
> reg-names is discouraged.  Please remove.  I always point people here
> as a reference:
>
> https://lore.kernel.org/r/CAL_Jsq+MMunmVWqeW9v2RyzsMKP+=kMzeTHNMG4JDHM7Fy0HBg@xxxxxxxxxxxxxx/
>
> You can just figure out whether there are 3 register fields or 1 register field.

Am not sure if I understand this correctly, reg-names are very useful in 
this particular case as we are dealing with multiple memory ranges with 
holes. I agree with not having this for cases where we have only one 
resource.

But having the ordering in DT without proper names associated with it 
seems fragile to me! And it makes very difficult to debug issues with 
wrong resource ordering in DT.

Rob, Is this the guidance for new bindings?

I have not seen any strong suggestion or guidance either in

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/resource-names.txt?h=v5.8-rc1 
 Or in ./drivers/of/address.c

Am I missing anything here?