linux-kernel - Re: [PATCH/RFC 0/4] dmaengine: add DT support for DMA multiplexers

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Date:	Tue, 30 Apr 2013 16:13:54 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Guennadi Liakhovetski <g.liakhovetski@....de>
Cc:	linux-sh@...r.kernel.org, Magnus Damm <magnus.damm@...il.com>,
	Arnd Bergmann <arnd@...db.de>,
	Tony Lindgren <tony@...mide.com>,
	devicetree-discuss@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	Guennadi Liakhovetski <g.liakhovetski+renesas@...il.com>
Subject: Re: [PATCH/RFC 0/4] dmaengine: add DT support for DMA multiplexers

On Tue, Apr 30, 2013 at 09:11:19AM +0200, Guennadi Liakhovetski wrote:
> Previously an issue has been discussed, arising on sh-/r-mobile ARM-based 
> systems. There we typically have multiple DMA controller instances with 
> exactly equal or very similar capabilities. Each of them can serve the same 
> slaves, using the same slave identifiers (request line IDs). With the 
> present DMA DT implementation _each_ such DMA slave would have to reference 
> _each_ of those DMA controllers in its DMA bindings, e.g.
But why... if that is the case then we havent define DT-bindings clearly enough

And we havent merged that yet, so why not fix that in first set itself

--
~Vinod
> 
> 	mmc0: mmc@...00000 {
> 		...
> 		dmas = <&dma0 0x10
> 			&dma1 0x10
> 			&dma2 0x10
> 			&dma3 0x10
> 			&dma0 0x11
> 			&dma1 0x11
> 			&dma2 0x11
> 			&dma3 0x11>;
> 		dma-names = "tx", "tx", "tx", "tx",
> 			"rx", "rx", "rx", "rx";
> 	};
> 
> Which certainly isn't pretty. To avoid such redundancy it has been proposed 
> to implement a DMA multiplexer DT node. That way slaves would just 
> reference the multiplexer and one of DMA controller instances in it would 
> be picked up automatically to provide DMA channels to slaves. Patches 1-3 
> in this series propose such an implementation. Patch 4 is just a minor 
> clean up, can be applied independently.
> 
> Cc: Guennadi Liakhovetski <g.liakhovetski+renesas@...il.com>
> 
> Guennadi Liakhovetski (4):
>   OF: add a new phandle parsing function for grouped nodes
>   dmaengine: add support for DMA multiplexer DT nodes
>   ARM: shmobile: move r8a7740 DMA controller DT node under a "dma-mux"
>     node
>   OF: modify function stubs to match proper function declarations.
> 
>  Documentation/devicetree/bindings/dma/dma.txt      |   44 ++++++++++++++++++++
>  .../boot/dts/r8a7740-armadillo800eva-reference.dts |   12 +++---
>  arch/arm/boot/dts/r8a7740.dtsi                     |   43 +++++++++++--------
>  drivers/dma/of-dma.c                               |   39 +++++++++++++----
>  drivers/of/base.c                                  |   28 +++++++++++-
>  include/linux/of.h                                 |   20 ++++++++-
>  6 files changed, 147 insertions(+), 39 deletions(-)
> 
> -- 
> 1.7.2.5
> 
> Thanks
> Guennadi
> ---
> Guennadi Liakhovetski, Ph.D.
> Freelance Open-Source Software Developer
> http://www.open-technology.de/
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