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

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Message-ID: <CAL_JsqLO_L+rTZh70nrpBMU1+CYKct7HhNY0gLGUnU7=JVRuQw@mail.gmail.com>
Date:   Wed, 21 Nov 2018 14:52:29 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>
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 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.

Rob