linux-kernel - Re: [PATCH v11 1/4] dt-bindings: dmaengine: Add doc for tegra gpcdma

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Message-ID: <CAL_JsqKqG79kZCT97pRnDHxztoq6rfJ9LDjn_iiuyvQksNnR4A@mail.gmail.com>
Date:   Thu, 18 Nov 2021 17:35:09 -0600
From:   Rob Herring <robh@...nel.org>
To:     Akhil R <akhilrajeev@...dia.com>
Cc:     "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Krishna Yarlagadda <kyarlagadda@...dia.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        "p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
        Rajesh Gumasta <rgumasta@...dia.com>,
        "thierry.reding@...il.com" <thierry.reding@...il.com>,
        "vkoul@...nel.org" <vkoul@...nel.org>
Subject: Re: [PATCH v11 1/4] dt-bindings: dmaengine: Add doc for tegra gpcdma

On Wed, Nov 3, 2021 at 5:34 AM Akhil R <akhilrajeev@...dia.com> wrote:
>
> > On Thu, Oct 28, 2021 at 06:53:36PM +0530, Akhil R wrote:
> > > Add DT binding document for Nvidia Tegra GPCDMA controller.
> > >
> > > Signed-off-by: Rajesh Gumasta <rgumasta@...dia.com>
> > > Signed-off-by: Akhil R <akhilrajeev@...dia.com>
> > > Reviewed-by: Jon Hunter <jonathanh@...dia.com>
> > > ---
> > >  .../bindings/dma/nvidia,tegra186-gpc-dma.yaml      | 115
> > +++++++++++++++++++++
> > >  1 file changed, 115 insertions(+)
> > >  create mode 100644
> > > Documentation/devicetree/bindings/dma/nvidia,tegra186-gpc-dma.yaml
> > >
> > > diff --git
> > > a/Documentation/devicetree/bindings/dma/nvidia,tegra186-gpc-dma.yaml
> > > b/Documentation/devicetree/bindings/dma/nvidia,tegra186-gpc-dma.yaml
> > > new file mode 100644
> > > index 0000000..bc97efc
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/dma/nvidia,tegra186-gpc-dma.ya
> > > +++ ml
> > > @@ -0,0 +1,115 @@
> > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) %YAML 1.2
> > > +---
> > > +$id: http://devicetree.org/schemas/dma/nvidia,tegra186-gpc-dma.yaml#
> > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > +
> > > +title: NVIDIA Tegra GPC DMA Controller Device Tree Bindings
> > > +
> > > +description: |
> > > +  The Tegra General Purpose Central (GPC) DMA controller is used for
> > > +faster
> > > +  data transfers between memory to memory, memory to device and
> > > +device to
> > > +  memory.
> > > +
> > > +maintainers:
> > > +  - Jon Hunter <jonathanh@...dia.com>
> > > +  - Rajesh Gumasta <rgumasta@...dia.com>
> > > +
> > > +allOf:
> > > +  - $ref: "dma-controller.yaml#"
> > > +
> > > +properties:
> > > +  compatible:
> > > +    oneOf:
> > > +      - enum:
> > > +          - nvidia,tegra186-gpcdma
> > > +          - nvidia,tegra194-gpcdma
> > > +      - items:
> > > +          - const: nvidia,tegra186-gpcdma
> > > +          - const: nvidia,tegra194-gpcdma
> >
> > One of these is wrong. Either 186 has a fallback to 194 or it doesn't.
> Not sure if I understood this correctly. Tegra186 and 194 have different chip data
> inside driver based on the compatible. I guess, it then needs to be one of these.
> Or is the mistake something related to formatting?

It's not about what the driver uses, but what is valid in a DT file.
Either you say the 2 implementations are different and in no way
compatible with each other:

enum:
  - nvidia,tegra186-gpcdma
  - nvidia,tegra194-gpcdma

Or you say 186 is backwards compatible with 194 (meaning 186 is a
superset of 194 so a driver written for 194 still works on 186 (though
not any new features)).

oneOf:
  - const: nvidia,tegra194-gpcdma
  - items:
    - const: nvidia,tegra186-gpcdma
    - const: nvidia,tegra194-gpcdma

Rob