linux-kernel - RE: [PATCH v4 1/4] dt-bindings: dmaengine: Add doc for tegra gpcdma

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Message-ID: <BN9PR12MB5273B8EC67EEC1D97DE9A7ECC0DB9@BN9PR12MB5273.namprd12.prod.outlook.com>
Date:   Wed, 15 Sep 2021 08:08:17 +0000
From:   Akhil R <akhilrajeev@...dia.com>
To:     Jonathan Hunter <jonathanh@...dia.com>
CC:     "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        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 v4 1/4] dt-bindings: dmaengine: Add doc for tegra gpcdma

> On 08/09/2021 15:32, 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>
> > ---
> >   .../bindings/dma/nvidia,tegra186-gpc-dma.yaml      | 106
> +++++++++++++++++++++
> >   1 file changed, 106 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..00c5582
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/dma/nvidia,tegra186-gpc-dma.ya
> > +++ ml
> > @@ -0,0 +1,106 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) %YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/dma/nvidia,tegra-gpc-dma.yaml#
> 
> tegra186-gpc-dma.yaml
> 
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Nvidia Tegra GPC DMA Controller Device Tree Bindings
> > +
> > +description: |
> > +  Tegra GPC DMA is the Genernal Purpose Central (GPC) DMA controller
> > +used for faster data
> 
> s/Genernal/General
> 
> I would just say
> 
> "The Tegra General Purpose Central (GPC) DMA controller is used for ..."
> 
> Over 80 characters. I assume that yaml files have that limitation.
> 
> > +  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:
> > +  "#dma-cells":
> > +    const: 1
> > +
> > +  compatible:
> > +    - enum:
> > +      - nvidia,tegra186-gpcdma
> > +      - nvidia,tegra194-gpcdma
> > +
> > +  reg:
> > +    maxItems: 1
> > +
> > +  interrupts:
> > +	minItems: 1
> > +    maxItems: 32
> 
> You appear to have alignment issues again.
> 
> > +
> > +  resets:
> > +    maxItems: 1
> > +
> > +  reset-names:
> > +    const: gpcdma
> > +
> > +  iommus:
> > +    maxItems: 1
> > +
> > +  nvidia,stream-id:
> > +	description: |
> > +	 stream-id corresponding to GPC DMA clients.
> > +	 Defaults to TEGRA186_SID_GPCDMA_0 if not given
> 
> 
> Why do we need this? Don't we already have the SID in the iommu property?
> 
> Jon

The value is required to be written to the register TEGRA_GPCDMA_CHAN_MCSEQ of the DMA controller (in function tegra_dma_program_sid) for the DMA to work as expected. I could not identify an api which can take the value from 'iommus' property.

Regards,
Akhil

> 
> --
> nvpublic