linux-kernel - Re: [PATCH 1/2] ARM: dts: spear13xx: Update SPI dma properties

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Message-ID: <CAK8P3a1Go8xiQG=BLBmqoQiVqwkcR+T8gi0WLijzVfa3A_WuKA@mail.gmail.com>
Date:   Mon, 14 Mar 2022 11:27:05 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Kuldeep Singh <singh.kuldeep87k@...il.com>,
        SoC Team <soc@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Viresh Kumar <vireshk@...nel.org>,
        Shiraz Hashim <shiraz.linux.kernel@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        DTML <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] ARM: dts: spear13xx: Update SPI dma properties

On Mon, Mar 14, 2022 at 8:31 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> On 14-03-22, 12:24, Kuldeep Singh wrote:
> > Dma-names order matters here.
> > As per pl022 binding, dma-names order specify rx,tx and all DTs which
> > have tx,rx as order start raising dtbs_chek warning. Thus, need to
> > reverse this order. Please note, no functional change in this patch
> > apart from just fixing warning.
> >
> > Warning:
> > 'rx' was expected
> > 'tx' was expected
>
> Hmm. I see your point now.
>
>   dma-names:
>     description:
>       There must be at least one channel named "tx" for transmit and named "rx"
>       for receive.
>     minItems: 2
>     maxItems: 32
>     additionalItems: true
>     items:
>       - const: rx
>       - const: tx
>
>
> I was expecting above to allow adding the items in any order, but
> looks like the order is fixed with this.

I don't think that it was meant to have a fixed order: unlike the other
bindings that define xxx-names properties, dmas require giving
names to allow the DT to specify more than one possible DMA
specifier for a given name. This means that nothing may ever just
rely on an index but has to use the name for lookup.

OTOH, while fixing the order in the binding does not add any
value, it's also harmless as this should never be able to break
anything that worked for any combination of old/new dtb and
kernel, and it's probably easier to express in the binding.

       Arnd