linux-kernel - RE: [PATCH v4 3/7] dt-bindings: dma: rz-dmac: Document RZ/V2H(P) family of SoCs

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Message-ID:
 <TYCPR01MB12093D1484AD0E755B76FAE35C2CC2@TYCPR01MB12093.jpnprd01.prod.outlook.com>
Date: Fri, 28 Feb 2025 14:55:34 +0000
From: Fabrizio Castro <fabrizio.castro.jz@...esas.com>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
CC: Vinod Koul <vkoul@...nel.org>, Rob Herring <robh@...nel.org>, Krzysztof
 Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, Magnus
 Damm <magnus.damm@...il.com>, Biju Das <biju.das.jz@...renesas.com>,
	"dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-renesas-soc@...r.kernel.org" <linux-renesas-soc@...r.kernel.org>,
	Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: RE: [PATCH v4 3/7] dt-bindings: dma: rz-dmac: Document RZ/V2H(P)
 family of SoCs

Hi Geert,

Thanks for your feedback!

> From: Geert Uytterhoeven <geert@...ux-m68k.org>
> Sent: 28 February 2025 10:17
> Subject: Re: [PATCH v4 3/7] dt-bindings: dma: rz-dmac: Document RZ/V2H(P) family of SoCs
> 
> Hi Fabrizio,
> 
> On Thu, 27 Feb 2025 at 19:16, Fabrizio Castro
> <fabrizio.castro.jz@...esas.com> wrote:
> > > From: Geert Uytterhoeven <geert@...ux-m68k.org>
> > > Sent: 24 February 2025 12:44
> > > Subject: Re: [PATCH v4 3/7] dt-bindings: dma: rz-dmac: Document RZ/V2H(P) family of SoCs
> > >
> > > On Thu, 20 Feb 2025 at 16:01, Fabrizio Castro
> > > <fabrizio.castro.jz@...esas.com> wrote:
> > > > Document the Renesas RZ/V2H(P) family of SoCs DMAC block.
> > > > The Renesas RZ/V2H(P) DMAC is very similar to the one found on the
> > > > Renesas RZ/G2L family of SoCs, but there are some differences:
> > > > * It only uses one register area
> > > > * It only uses one clock
> > > > * It only uses one reset
> > > > * Instead of using MID/IRD it uses REQ NO/ACK NO
> > > > * It is connected to the Interrupt Control Unit (ICU)
> > > >
> > > > Signed-off-by: Fabrizio Castro <fabrizio.castro.jz@...esas.com>
> > >
> > > > v1->v2:
> > > > * Removed RZ/V2H DMAC example.
> > > > * Improved the readability of the `if` statement.
> > >
> > > Thanks for the update!
> > >
> > > > --- a/Documentation/devicetree/bindings/dma/renesas,rz-dmac.yaml
> > > > +++ b/Documentation/devicetree/bindings/dma/renesas,rz-dmac.yaml
> > > > @@ -61,14 +66,22 @@ properties:
> > > >    '#dma-cells':
> > > >      const: 1
> > > >      description:
> > > > -      The cell specifies the encoded MID/RID values of the DMAC port
> > > > -      connected to the DMA client and the slave channel configuration
> > > > -      parameters.
> > > > +      For the RZ/A1H, RZ/Five, RZ/G2{L,LC,UL}, RZ/V2L, and RZ/G3S SoCs, the cell
> > > > +      specifies the encoded MID/RID values of the DMAC port connected to the
> > > > +      DMA client and the slave channel configuration parameters.
> > > >        bits[0:9] - Specifies MID/RID value
> > > >        bit[10] - Specifies DMA request high enable (HIEN)
> > > >        bit[11] - Specifies DMA request detection type (LVL)
> > > >        bits[12:14] - Specifies DMAACK output mode (AM)
> > > >        bit[15] - Specifies Transfer Mode (TM)
> > > > +      For the RZ/V2H(P) SoC the cell specifies the REQ NO, the ACK NO, and the
> > > > +      slave channel configuration parameters.
> > > > +      bits[0:9] - Specifies the REQ NO
> > >
> > > So REQ_NO is the new name for MID/RID.
> 
> These are documented in Table 4.7-22 ("DMA Transfer Request Detection
> Operation Setting Table").

REQ_NO is documented in both Table 4.7-22 and in Table 4.6-23 (column `DMAC No.`).

> 
> > It's certainly similar. I would say that REQ_NO + ACK_NO is the new MID_RID.
> >
> > > > +      bits[10:16] - Specifies the ACK NO
> > >
> > > This is a new field.
> > > However, it is not clear to me which value to specify here, and if this
> > > is a hardware property at all, and thus needs to be specified in DT?
> >
> > It is a HW property. The value to set can be found in Table 4.6-27 from
> > the HW User Manual, column "Ack No".
> 
> Thanks, but that table only shows values for SPDIF, SCU, SSIU and PFC
> (for external DMA requests).  The most familiar DMA clients listed
> in Table 4.7-22 are missing.  E.g. RSPI0 uses REQ_NO 0x8C/0x8D, but
> which values does it need for ACK_NO?

Only a handful of devices need it. For every other device (and use case) only the
default value is needed.

But I'll take this out for now, until we get to support a device that actually
needs ACK NO.

Thanks!

Fab

> 
> 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