linux-kernel - Re: [PATCH 1/7] dmaengine: st_fdma: Add STMicroelectronics FDMA DT binding documentation

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Date:	Thu, 3 Sep 2015 10:18:54 +0100
From:	Peter Griffin <peter.griffin@...aro.org>
To:	Lee Jones <lee.jones@...aro.org>
Cc:	Vinod Koul <vinod.koul@...el.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	srinivas.kandagatla@...il.com, maxime.coquelin@...com,
	patrice.chotard@...com, dan.j.williams@...el.com,
	devicetree@...r.kernel.org, dmaengine@...r.kernel.org,
	ludovic.barre@...com
Subject: Re: [PATCH 1/7] dmaengine: st_fdma: Add STMicroelectronics FDMA DT
 binding documentation

Hi Lee,

On Wed, 26 Aug 2015, Lee Jones wrote:

> On Tue, 25 Aug 2015, Peter Griffin wrote:
> 
> > Hi Vinod,
> > 
> > Thanks for reviewing.
> > 
> > On Wed, 19 Aug 2015, Vinod Koul wrote:
> > 
> > > On Wed, Jul 08, 2015 at 05:11:22PM +0100, Peter Griffin wrote:
> > > > This patch adds the DT binding documentation for the FDMA constroller
> > > > found on STi based chipsets from STMicroelectronics.
> > > > 
> > > > Signed-off-by: Ludovic Barre <ludovic.barre@...com>
> > > > Signed-off-by: Peter Griffin <peter.griffin@...aro.org>
> > > > ---
> > > >  Documentation/devicetree/bindings/dma/st_fdma.txt | 76 +++++++++++++++++++++++
> > > >  1 file changed, 76 insertions(+)
> > > >  create mode 100644 Documentation/devicetree/bindings/dma/st_fdma.txt
> > > > 
> > > > diff --git a/Documentation/devicetree/bindings/dma/st_fdma.txt b/Documentation/devicetree/bindings/dma/st_fdma.txt
> > > > new file mode 100644
> > > > index 0000000..1ec7470
> > > > --- /dev/null
> > > > +++ b/Documentation/devicetree/bindings/dma/st_fdma.txt
> > > > @@ -0,0 +1,76 @@
> > > > +* STMicroelectronics Flexible Direct Memory Access Device Tree bindings
> > > > +
> > > > +The FDMA is a general-purpose direct memory access controller capable of
> > > > +supporting 16 independent DMA channels. It accepts up to 32 DMA requests.
> > > > +The FDMA is based on a Slim processor which require a firmware.
> > > > +
> > > > +* FDMA Controller
> > > > +
> > > > +Required properties:
> > > > +- compatible	: Should be "st,fdma_mpe31"
> > > > +- reg		: Should contain DMA registers location and length
> > > > +- interrupts	: Should contain one interrupt shared by all channel
> > > 
> > > s/channel/channels
> > 
> > Will fix in v2.
> > 
> > > 
> > > > +- dma-channels	: Number of channels supported by the controller
> > > > +- #dma-cells	: Must be <3>.
> > > 
> > > any reason three?
> > 
> > Yes, it is documented further down in the file under DMA Client.
> > 
> > To make it clearer in V2 I could change to
> > 
> > "- #dma-cells	: Must be <3>. See DMA client section below"?
> 
> - #dma-cells	: Must be <3>
> 			1st cell: Phandle to       ... <blah>
> 			2nd cell: DMA channel      ... <blah>
> 			3rd cell: Flags describing ... <blah>  

I'd prefer not to document it twice in the same file as it is
almost 20 lines long. IMHO it makes more sense to document it under
the dma-client section like it is done presently, because when writing a
dma-client node you need to know what these things mean.

When writing a controller node all you only need to know is
"Must be <3>". A more avid reader now has a nice pointer to scroll
down if they wish to find out more.

regards,

Peter.
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