linux-kernel - Re: [PATCH 07/15] dmaengine: dw: revisit data

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Date:	Mon, 25 Jan 2016 12:36:50 +0200
From:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:	Måns Rullgård <mans@...sr.com>
Cc:	Vineet Gupta <Vineet.Gupta1@...opsys.com>,
	Viresh Kumar <vireshk@...nel.org>,
	Vinod Koul <vinod.koul@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Russell King <linux@....linux.org.uk>,
	Dan Williams <dan.j.williams@...el.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-snps-arc@...ts.infradead.org" 
	<linux-snps-arc@...ts.infradead.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 07/15] dmaengine: dw: revisit data_width property

On Mon, 2016-01-25 at 10:31 +0000, Måns Rullgård wrote:
> Andy Shevchenko <andriy.shevchenko@...ux.intel.com> writes:
> 
> > On Mon, 2016-01-25 at 07:32 +0000, Vineet Gupta wrote:
> > > On Monday 25 January 2016 12:55 AM, Mans Rullgard wrote:

> > > > --- a/Documentation/devicetree/bindings/dma/snps-dma.txt
> > > > +++ b/Documentation/devicetree/bindings/dma/snps-dma.txt
> > > > @@ -13,8 +13,7 @@ Required properties:
> > > >  - chan_priority: priority of channels. 0 (default): increase
> > > > from
> > > > chan 0->n, 1:
> > > >    increase from chan n->0
> > > >  - block_size: Maximum block size supported by the controller
> > > > -- data_width: Maximum data width supported by hardware per AHB
> > > > master
> > > > -  (0 - 8bits, 1 - 16bits, ..., 5 - 256bits)
> > > > +- data-width: Maximum data width supported by hardware (in
> > > > bytes)
> > > 
> > > To the reader this suggests a value truely byte granular, but
> > > code
> > > uses ffs
> > > implying that it is still power of 2.
> > > Can you mention this here (....in bytes, always power of 2).
> > 
> > While this comment is good, I have still note that using non-power
> > of 2
> > values will not break anything. Least power of two number will be
> > used
> > in that case. So, means I would suggest to replace 'always' by
> > 'better
> > to be' or something like that.
> 
> Although the code rounds down, the hardware actually works in powers
> of
> two, and it's better to document this.

Let's do "(in bytes, power of 2)" then?

-- 
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy