linux-kernel - Re: [PATCH 2/3] dt-bindings: mfd: atmel-usart: add DMA bindings for SPI mode

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Message-ID: <20181121212157.GD12656@piout.net>
Date:   Wed, 21 Nov 2018 22:21:57 +0100
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     radu_nicolae.pirea@....ro,
        Richard Genoud <richard.genoud@...il.com>,
        Lee Jones <lee.jones@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Ludovic Desroches <ludovic.desroches@...rochip.co>,
        Mark Brown <broonie@...nel.org>, devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        linux-spi <linux-spi@...r.kernel.org>
Subject: Re: [PATCH 2/3] dt-bindings: mfd: atmel-usart: add DMA bindings for
 SPI mode

On 21/11/2018 14:52:29-0600, Rob Herring wrote:
> On Wed, Nov 21, 2018 at 10:48 AM Alexandre Belloni
> <alexandre.belloni@...tlin.com> wrote:
> >
> > Hi Rob,
> >
> > On 21/11/2018 10:41:01-0600, Rob Herring wrote:
> > > > +Optional properties in serial and SPI mode:
> > > > +- dma bindings for dma transfer:
> > > > +       - dmas: DMA specifier, consisting of a phandle to DMA controller node,
> > > > +               memory peripheral interface and USART DMA channel ID, FIFO configuration.
> > > > +               Refer to dma.txt and atmel-dma.txt for details.
> > > > +       - dma-names: "rx" for RX channel, "tx" for TX channel.
> > >
> > > > +               dma-names = "tx", "rx";
> > >
> > > The dma-names should have a defined order.
> > >
> >
> > Why is that? Isn't the purpose of names to get rid of any particular
> > ordering?
> 
> Because a fundamental rule of DT is the order is defined and
> important. The purpose was to allow for cases that had a variable
> number of entries, but even a variable number still have a defined
> order.
> 

Thank you for the clarification!


-- 
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com