linux-kernel - Re: [PATCH 1/2] arm64: dts: renesas: r9a09g056: Add DMA support for RSPI channels

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Message-ID: <CA+V-a8vqVm9-kO_hMhN5WcsEXamUU8=hafGFzmsbKXFwv0UL_g@mail.gmail.com>
Date: Thu, 8 Jan 2026 13:25:42 +0000
From: "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Magnus Damm <magnus.damm@...il.com>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	linux-renesas-soc@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Biju Das <biju.das.jz@...renesas.com>, 
	Fabrizio Castro <fabrizio.castro.jz@...esas.com>, 
	Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [PATCH 1/2] arm64: dts: renesas: r9a09g056: Add DMA support for
 RSPI channels

Hi Geert,

Thank you for the review.

On Thu, Jan 8, 2026 at 1:18 PM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>
> Hi Prabhakar,
>
> On Mon, 15 Dec 2025 at 17:34, Prabhakar <prabhakar.csengg@...il.com> wrote:
> > From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> >
> > Enable DMA support for RSPI channels.
> >
> > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
>
> Thanks for your patch!
>
> > --- a/arch/arm64/boot/dts/renesas/r9a09g056.dtsi
> > +++ b/arch/arm64/boot/dts/renesas/r9a09g056.dtsi
> > @@ -679,6 +679,8 @@ rspi0: spi@...00000 {
> >                         clock-names = "pclk", "pclk_sfr", "tclk";
> >                         resets = <&cpg 0x7b>, <&cpg 0x7c>;
> >                         reset-names = "presetn", "tresetn";
> > +                       dmas = <&dmac0 0x448c>, <&dmac0 0x448d>;
> > +                       dma-names = "rx", "tx";
>
> RZ/V2N does not seem to have restrictions about which DMA controllers
> can be used by which SPI instance.  Hence shouldn't these point to
> all five DMA controllers?
>
>     dmas = <&dmac0 0x448c>, <&dmac0 0x448d>,
>            <&dmac1 0x448c>, <&dmac1 0x448d>,
>            <&dmac2 0x448c>, <&dmac2 0x448d>,
>            <&dmac3 0x448c>, <&dmac3 0x448d>,
>            <&dmac4 0x448c>, <&dmac4 0x448d>;
>     dma-names = "rx", "tx", "rx", "tx", "rx", "tx",
>                 "rx", "tx", "rx", "tx";
>
So the driver would choose the DMA channel based on the available one?
For example if all the 16 channels are consumed for dmac0 the driver
would switch to the next available one dmacX? and this would be the
job of a consumer driver? Or do we want to let the board user
choose/override in board DTS based on the available DMAC channels?

> Note that this requires updating the DT bindings, as they currently
> restrict dma to two entries.
>
Agreed.

Cheers,
Prabhakar

> >                         power-domains = <&cpg>;
> >                         #address-cells = <1>;
> >                         #size-cells = <0>;
>
> The actual DMA specifier values are OK, 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