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

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Message-ID:
 <TYYPR01MB139556681F53AC66A668F7E4D85B5A@TYYPR01MB13955.jpnprd01.prod.outlook.com>
Date: Tue, 23 Dec 2025 14:42:21 +0000
From: Cosmin-Gabriel Tanislav <cosmin-gabriel.tanislav.xa@...esas.com>
To: geert <geert@...ux-m68k.org>
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

> From: Geert Uytterhoeven <geert@...ux-m68k.org>
> Sent: Tuesday, December 23, 2025 4:25 PM
> 
> Hi Cosmin,
> 
> 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?

> The rest LGTM, so
> Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>
> 
> 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