linux-kernel - Re: [PATCH v1] dt-bindings: dma: st-stm32-dmamux: Add description for dma-cell values

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Message-ID: <CADRqkYDnDNL_H2CzxjsPOdM++iYp-9Ak3PVFBw2qcjR_M=GeBA@mail.gmail.com>
Date: Thu, 5 Dec 2024 11:07:20 -0500
From: Ken Sloat <ksloat@...nersoftsolutions.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	devicetree@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com, 
	dmaengine@...r.kernel.org, alexandre.torgue@...s.st.com, 
	mcoquelin.stm32@...il.com, conor+dt@...nel.org, krzk+dt@...nel.org, 
	robh@...nel.org, vkoul@...nel.org, amelie.delaunay@...s.st.com, 
	Ken Sloat <ksloat@...nersoftsolutions.com>
Subject: Re: [PATCH v1] dt-bindings: dma: st-stm32-dmamux: Add description for
 dma-cell values

Hi Krzysztof,

Thanks for reviewing

On Thu, Dec 5, 2024 at 10:59 AM Krzysztof Kozlowski <krzk@...nel.org> wrote:
>
> On 05/12/2024 16:32, Ken Sloat wrote:
> > The dma-cell values for the stm32-dmamux are used to craft the DMA spec
> > for the actual controller. These values are currently undocumented
> > leaving the user to reverse engineer the driver in order to determine
> > their meaning. Add a basic description, while avoiding duplicating
> > information by pointing the user to the associated DMA docs that
> > describe the fields in depth.
> >
> > Signed-off-by: Ken Sloat <ksloat@...nersoftsolutions.com>
> > ---
> > .../bindings/dma/stm32/st,stm32-dmamux.yaml | 11 +++++++++++
> > 1 file changed, 11 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/dma/stm32/st,stm32-dmamux.yaml
> > b/Documentation/devicetree/bindings/dma/stm32/st,stm32-dmamux.yaml
> > index f26c914a3a9a..aa2e52027ee6 100644
> > --- a/Documentation/devicetree/bindings/dma/stm32/st,stm32-dmamux.yaml
> > +++ b/Documentation/devicetree/bindings/dma/stm32/st,stm32-dmamux.yaml
> > @@ -15,6 +15,17 @@ allOf:
> > properties:
> > "#dma-cells":
> > const: 3
>
> Your patch is corrupted. Please use git send-email or b4 or b4+relay.

Sorry about that, I will do that. I will wait for any additional
comments and then re-submit.

>
> > + description: |
> > + Should be set to <3> with each cell representing the following:
>
> Drop this part, const says this.

Ok

>
> > + 1. The mux input number/line for the request
> > + 2. Bitfield representing DMA channel configuration that is passed
> > + to the real DMA controller
> > + 3. Bitfield representing device dependent DMA features passed to
> > + the real DMA controller
> > +
> > + For bitfield definitions of cells 2 and 3, see the associated
> > + bindings doc for the actual DMA controller the mux is connected
>
> This does not sound right. This is the binding for DMA controller, so
> you are saying "please look at itself". I suggest to drop this as well.
>

While logically it is the DMA controller, this doc is specifically for
the mux - the DMA controller has its own driver and binding docs in
Documentation/devicetree/bindings/dma/stm32/st,stm32-dma.yaml

I can reference st,stm32-dma.yaml directly, but I was unsure if this
mux IP was used with another DMA controller from ST on a different
SoC.

What do you suggest here?

>
> Best regards,
> Krzysztof

-- 
Sincerely,
Ken Sloat