linux-kernel - Re: [PATCH 1/2] dma: of: Remove restriction that #dma-cells can't be 0

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Message-Id: <201304221654.38159.arnd@arndb.de>
Date:	Mon, 22 Apr 2013 16:54:37 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	"Lars-Peter Clausen" <lars@...afoo.de>
Cc:	Vinod Koul <vinod.koul@...el.com>, Jon Hunter <jon-hunter@...com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] dma: of: Remove restriction that #dma-cells can't be 0

On Monday 22 April 2013, Lars-Peter Clausen wrote:
> 
> On 04/22/2013 02:38 PM, Arnd Bergmann wrote:
> > On Monday 22 April 2013, Lars-Peter Clausen wrote:
> >>
> >> There is no sensible reason why #dma-cells shouldn't be allowed to be 0. It is
> >> completely up to the DMA controller how many additional parameters, besides the
> >> phandle, it needs to identify a channel. E.g. for DMA controller with only one
> >> channel or for DMA controllers which don't have a restriction on which channel
> >> can be used for which peripheral it completely legitimate to not require any
> >> additional parameters.
> >>
> >> Also fixes the following warning:
> >>         drivers/dma/of-dma.c: In function 'of_dma_controller_register':
> >>         drivers/dma/of-dma.c:67:7: warning: 'nbcells' may be used uninitialized in this function
> >>
> >> Signed-off-by: Lars-Peter Clausen <lars@...afoo.de>
> > 
> > Do you have an example for this? If a dma engine has only one request line,
> > why would you even use the dmaengine subsystem for it, rather than including
> > the code to program it in the slave driver?
> 
> Why wouldn't I use the dmaengine subsystem for a DMA controller? In my
> particular case different instances of the same DMA core will be used with
> different DMA slaves. And the DMA slaves can also have different DMA master
> cores, depending on the system.

Right, that makes sense.

Acked-by: Arnd Bergmann <arnd@...db.de>
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