linux-kernel - Re: [PATCH 12/13] arm64: dts: renesas: r9a09g077: wire up DMA support for SPI

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Message-ID: <CAMuHMdUeoC7OefbLd+0WihUtvV7zMtFREeor+V3efUitzcgiZw@mail.gmail.com>
Date: Tue, 23 Dec 2025 17:04:09 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Cosmin-Gabriel Tanislav <cosmin-gabriel.tanislav.xa@...esas.com>
Cc: Fabrizio Castro <fabrizio.castro.jz@...esas.com>, Mark Brown <broonie@...nel.org>, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Geert Uytterhoeven <geert+renesas@...der.be>, "magnus.damm" <magnus.damm@...il.com>, 
	Philipp Zabel <p.zabel@...gutronix.de>, 
	"linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>, 
	"linux-renesas-soc@...r.kernel.org" <linux-renesas-soc@...r.kernel.org>, 
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 12/13] arm64: dts: renesas: r9a09g077: wire up DMA support
 for SPI

Hi Cosmin,

On Tue, 23 Dec 2025 at 15:42, Cosmin-Gabriel Tanislav
<cosmin-gabriel.tanislav.xa@...esas.com> wrote:
> > From: Geert Uytterhoeven <geert@...ux-m68k.org>
> > On Mon, 1 Dec 2025 at 14:44, Cosmin Tanislav
> > <cosmin-gabriel.tanislav.xa@...esas.com> wrote:
> > > RZ/T2H (R9A09G077) has three DMA controllers that can be used by
> > > peripherals like SPI to offload data transfers from the CPU.
> > >
> > > Wire up the DMA channels for the SPI peripherals.
> > >
> > > Signed-off-by: Cosmin Tanislav <cosmin-gabriel.tanislav.xa@...esas.com>
> >
> > Thanks for your patch!
> >
> > > --- a/arch/arm64/boot/dts/renesas/r9a09g077.dtsi
> > > +++ b/arch/arm64/boot/dts/renesas/r9a09g077.dtsi
> > > @@ -200,6 +200,8 @@ rspi0: spi@...07000 {
> > >                         clocks = <&cpg CPG_CORE R9A09G077_CLK_PCLKM>,
> > >                                  <&cpg CPG_MOD 104>;
> > >                         clock-names = "pclk", "pclkspi";
> > > +                       dmas = <&dmac0 0x267a>, <&dmac0 0x267b>;
> > > +                       dma-names = "rx", "tx";
> >
> > RZ/T2H does not seem to have restrictions about which DMA controllers
> > can be used by which SPI instance.  Hence shouldn't these point to
> > all three DMA controllers?
>
> It does seem like there's no restriction about which DMA controller to
> use.
>
> >     dmas = <&dmac0 0x267a>, <&dmac0 0x267b>,
> >            <&dmac1 0x267a>, <&dmac1 0x267b>,
> >            <&dmac2 0x267a>, <&dmac2 0x267b>;
> >     dma-names = "rx", "tx", "rx", "tx", "rx", "tx";
> >
>
> I was not aware that the DMA core supports this. I will add the other DMA
> controllers to the list.
>
> > Note that this requires updating the DT bindings, as they currently
> > restrict dma to two entries.
>
> dma-names:
>   items:
>     enum:
>       - rx
>       - tx
>
> This should work fine, right?

Yes, dma-names is OK.  But currently dmas has "maxItems: 2".

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds