linux-kernel - RE: [PATCH 1/2] spi: renesas,rzv2m-csi: Add SPI Slave related properties

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Message-ID: <TYWPR01MB8775BF850914BEFE55287486C2C2A@TYWPR01MB8775.jpnprd01.prod.outlook.com>
Date:   Wed, 27 Sep 2023 09:36:29 +0000
From:   Fabrizio Castro <fabrizio.castro.jz@...esas.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
CC:     Mark Brown <broonie@...nel.org>, Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Magnus Damm <magnus.damm@...il.com>,
        "linux-spi@...r.kernel.org" <linux-spi@...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>,
        Chris Paterson <Chris.Paterson2@...esas.com>,
        Biju Das <biju.das@...renesas.com>,
        Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: RE: [PATCH 1/2] spi: renesas,rzv2m-csi: Add SPI Slave related
 properties

Hi Geert,

Thanks for your reply!

> From: Geert Uytterhoeven <geert@...ux-m68k.org>
> Subject: Re: [PATCH 1/2] spi: renesas,rzv2m-csi: Add SPI Slave related
> properties
> 
> Hi Fabrizio,
> 
> On Tue, Sep 26, 2023 at 11:08 PM Fabrizio Castro
> <fabrizio.castro.jz@...esas.com> wrote:
> > The CSI IP found inside the Renesas RZ/V2M SoC can also work
> > in SPI slave mode.
> > When working in slave mode, the IP can make use of the SS
> > (Slave Select) pin, with "low" as default active level.
> > The active level of SS can be changed to "high" upon configuration.
> > This patch adds two new properties, one to make use of the
> > SS pin when in slave mode, and one to make the SS pin active high.
> >
> > Signed-off-by: Fabrizio Castro <fabrizio.castro.jz@...esas.com>
> 
> Thanks for your patch!
> 
> > --- a/Documentation/devicetree/bindings/spi/renesas,rzv2m-csi.yaml
> > +++ b/Documentation/devicetree/bindings/spi/renesas,rzv2m-csi.yaml
> > @@ -39,6 +39,17 @@ properties:
> >    power-domains:
> >      maxItems: 1
> >
> > +  renesas,csi-ss:
> > +    type: boolean
> > +    description:
> > +      Use CSI Slave Selection (SS) pin to enable transmission and
> reception when
> > +      in slave mode.
> 
> Can't this be done in a more generic way? I had expected that the
> existing SPI_NO_CS flag can be set using a property in the "slave"
> subnode,
> but apparently there is no "spi-no-cs" property defined yet.

I couldn't find a generic way to address that in a generic way.

> 
> > +
> > +  renesas,csi-ss-high:
> > +    type: boolean
> > +    description:
> > +      The SS pin is active high (by default the SS pin is active
> low).
> 
> Can't you use the "spi-cs-high" property in the "slave" subnode
> instead?

I could. I didn't go for it for the first version of this series
after reading the automatic handling of SPI_CS_HIGH (which for
example doesn't get automatically added to the mode for targets
using a GPIO as CS). Even though nothing prevents you from
explicitly adding SPI_CS_HIGH to the mode and using "spi-cs-high"
in the device tree, I thought that could be confusing, but
maybe it's not?

Thanks,
Fab

> 
> > +
> >  required:
> >    - compatible
> >    - reg
> 
> 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