linux-kernel - Re: [RFC 1/3] dt-bindings: dma: Add documentation for DMA domains

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Date:   Sun, 8 Sep 2019 17:40:58 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Peter Ujfalusi <peter.ujfalusi@...com>
Cc:     robh+dt@...nel.org, dmaengine@...r.kernel.org,
        linux-kernel@...r.kernel.org, dan.j.williams@...el.com,
        devicetree@...r.kernel.org
Subject: Re: [RFC 1/3] dt-bindings: dma: Add documentation for DMA domains

On 08-09-19, 10:47, Peter Ujfalusi wrote:
> 
> 
> On 06/09/2019 17.18, Peter Ujfalusi wrote:
> > On systems where multiple DMA controllers available, none Slave (for example
> > memcpy operation) users can not be described in DT as there is no device
> > involved from the DMA controller's point of view, DMA binding is not usable.
> > However in these systems still a peripheral might need to be serviced by or
> > it is better to serviced by specific DMA controller.
> > When a memcpy is used to/from a memory mapped region for example a DMA in the
> > same domain can perform better.
> > For generic software modules doing mem 2 mem operations it also matter that
> > they will get a channel from a controller which is faster in DDR to DDR mode
> > rather then from the first controller happen to be loaded.
> > 
> > This property is inherited, so it may be specified in a device node or in any
> > of its parent nodes.
> > 
> > Signed-off-by: Peter Ujfalusi <peter.ujfalusi@...com>
> > ---
> >  .../devicetree/bindings/dma/dma-domain.yaml   | 59 +++++++++++++++++++
> >  1 file changed, 59 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/dma/dma-domain.yaml
> > 
> > diff --git a/Documentation/devicetree/bindings/dma/dma-domain.yaml b/Documentation/devicetree/bindings/dma/dma-domain.yaml
> > new file mode 100644
> > index 000000000000..c2f182f30081
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/dma/dma-domain.yaml
> > @@ -0,0 +1,59 @@
> > +# SPDX-License-Identifier: GPL-2.0
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/dma/dma-controller.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: DMA Domain Controller Definition
> > +
> > +maintainers:
> > +  - Vinod Koul <vkoul@...nel.org>
> > +
> > +allOf:
> > +  - $ref: "dma-controller.yaml#"
> > +
> > +description:
> > +  On systems where multiple DMA controllers available, none Slave (for example
> > +  memcpy operation) users can not be described in DT as there is no device
> > +  involved from the DMA controller's point of view, DMA binding is not usable.
> > +  However in these systems still a peripheral might need to be serviced by or
> > +  it is better to serviced by specific DMA controller.
> > +  When a memcpy is used to/from a memory mapped region for example a DMA in the
> > +  same domain can perform better.
> > +  For generic software modules doing mem 2 mem operations it also matter that
> > +  they will get a channel from a controller which is faster in DDR to DDR mode
> > +  rather then from the first controller happen to be loaded.
> > +
> > +  This property is inherited, so it may be specified in a device node or in any
> > +  of its parent nodes.
> > +
> > +properties:
> > +  $dma-domain-controller:
> 
> or domain-dma-controller?

I feel dma-domain-controller sounds fine as we are defining domains for
dmaengine. Another thought which comes here is that why not extend this to
slave as well and define dma-domain-controller for them as use that for
filtering, that is what we really need along with slave id in case a
specific channel is to be used by a peripheral

Thoughts..?

-- 
~Vinod