linux-kernel - Re: [PATCH] dmaengine: imx-sdma: Add DMA event remapping for imx6sx-sdma

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Date:	Mon, 20 Apr 2015 10:34:33 -0700
From:	Nicolin Chen <nicoleotsuka@...il.com>
To:	Sascha Hauer <s.hauer@...gutronix.de>
Cc:	vinod.koul@...el.com, fabio.estevam@...escale.com,
	b38343@...escale.com, robh+dt@...nel.org, pawel.moll@....com,
	mark.rutland@....com, ijc+devicetree@...lion.org.uk,
	galak@...eaurora.org, dan.j.williams@...el.com,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	dmaengine@...r.kernel.org
Subject: Re: [PATCH] dmaengine: imx-sdma: Add DMA event remapping for
 imx6sx-sdma

Hi Sascha,

Thank you for the comments.

On Mon, Apr 20, 2015 at 11:45:41AM +0200, Sascha Hauer wrote:
> On Tue, Apr 14, 2015 at 10:39:11PM -0700, Nicolin Chen wrote:
> > The SDMA on imx6sx has a few DMA event remapping configurations
> > inside the GPR (General Purpose Register) of that SoC. When users
> > want to use a non-default DMA event, they need to configure the
> > GPR register. So this patch gives an interface of the GPR and
> > implements it in the SDMA driver so as to finish the DMA event
> > remapping.
> > 
> > Signed-off-by: Nicolin Chen <nicoleotsuka@...il.com>

> > diff --git a/Documentation/devicetree/bindings/dma/fsl-imx-sdma.txt b/Documentation/devicetree/bindings/dma/fsl-imx-sdma.txt
> > index dc8d3aa..03315a6 100644
> > --- a/Documentation/devicetree/bindings/dma/fsl-imx-sdma.txt
> > +++ b/Documentation/devicetree/bindings/dma/fsl-imx-sdma.txt
> > @@ -8,6 +8,7 @@ Required properties:
> >        "fsl,imx51-sdma"
> >        "fsl,imx53-sdma"
> >        "fsl,imx6q-sdma"
> > +      "fsl,imx6sx-sdma"
> >    The -to variants should be preferred since they allow to determine the
> >    correct ROM script addresses needed for the driver to work without additional
> >    firmware.
> > @@ -19,6 +20,14 @@ Required properties:
> >  - fsl,sdma-ram-script-name : Should contain the full path of SDMA RAM
> >    scripts firmware
> >  
> > +Optional properties:
> > +- fsl, sdma-event-remap : List of one or more DMA event remapping
> > +  configurations. Its format: <&gpr addr shift val>
> > +	gpr : the gpr phandle
> > +	addr : the register address of the GPR
> > +	shift : the bit shift of the GPR register
> > +	val : the value of that bit
> 
> This binding allows arbitrary register writes to the GPR register space.
> I don't think we want to allow that. A binding for this if necessary at
> all must be higher level.

I was actually wondering where could be the best place to put this in.
But I couldn't figure out a better place than this driver while being
worried about the violation as you mentioned.

But what could be that higher level?

Thank you
Nicolin
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