linux-kernel - Re: [PATCH v3 0/7] of: setup dma parameters using dma-ranges and dma-coherent

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Date:	Mon, 02 Jun 2014 21:00:16 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Santosh Shilimkar <santosh.shilimkar@...com>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Shawn Guo <shawn.guo@...escale.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"Strashko, Grygorii" <grygorii.strashko@...com>,
	Russell King <linux@....linux.org.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Olof Johansson <olof@...om.net>,
	Rob Herring <robh+dt@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Grant Likely <grant.likely@...aro.org>
Subject: Re: [PATCH v3 0/7] of: setup dma parameters using dma-ranges and dma-coherent

On Monday 02 June 2014 11:54:36 Santosh Shilimkar wrote:
> 
> On Monday 02 June 2014 11:06 AM, Arnd Bergmann wrote:
> > On Monday 02 June 2014 09:24:50 Santosh Shilimkar wrote:
> >> On Monday 02 June 2014 02:37 AM, Shawn Guo wrote:
> >>> On Thu, Apr 24, 2014 at 11:30:00AM -0400, Santosh Shilimkar wrote:
> >>>> Here is an updated v3 of the series. Series introduces support for setting up
> >>>> dma parameters based on device tree properties like 'dma-ranges' and
> >>>> 'dma-coherent' and also update to ARM 32 bit port. Earlier version of the
> >>>> series can be found here [3], [2] and [1].
> >>>
> >>> Are these two generic device tree properties documented somewhere under
> >>> Documentation/devicetree/bindings?
> >>>
> >> These bindings have been already in use before this series. But looks like
> >> they have not been documented. I will do a patch to add description for those
> >> couple of parameters.
> > 
> > dma-ranges is part of ePAPR, and was documented in some ieee-1275 addenda
> > before that, but I agree it would be nice to have something in kernel as
> > well, at the minimum something pointing to the relevant documents.
> > 
> We are thinking of updating 'Documentation/devicetree/bindings/dma/dma.txt'
> to add the information for these extra two parameters.
> 
> Is that fine or any other suggestion ?

I think that's the wrong place. That entire directory currently deals with
the specific case of DMA engines, as opposed to the more DMA bus mastering
in general. We could rename that to
Documentation/devicetree/bindings/dmaengine, but renames tend to cause
extra patch conficts, so I'd prefer finding another location for this.

How about a section in the top-level
Documentation/devicetree/booting-without-of.txt file? After all, this
is very generic and can impact any device that acts as a bus master.

	Arnd
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