Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:2 as permitted sender) client-ip=2620:137:e000::3:2;
Date:   Wed, 27 Sep 2023 11:21:54 +0200
From:   Mark Brown <broonie@kernel.org>
To:     Geert Uytterhoeven <geert@linux-m68k.org>
Cc:     Fabrizio Castro <fabrizio.castro.jz@renesas.com>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Conor Dooley <conor+dt@kernel.org>,
        Magnus Damm <magnus.damm@gmail.com>, linux-spi@vger.kernel.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-renesas-soc@vger.kernel.org,
        Chris Paterson <Chris.Paterson2@renesas.com>,
        Biju Das <biju.das@bp.renesas.com>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Subject: Re: [PATCH 1/2] spi: renesas,rzv2m-csi: Add SPI Slave related
 properties
Message-ID: <ZRP0MpIHf67tfQJY@finisterre.sirena.org.uk>
References: <20230926210818.197356-1-fabrizio.castro.jz@renesas.com>
 <20230926210818.197356-2-fabrizio.castro.jz@renesas.com>
 <CAMuHMdUibHxPBCLbeWdNrEk_szm+o4cOcskEMZAqUufNTzQKMQ@mail.gmail.com>
 <ZRPvHJXbuZ9Db2Go@finisterre.sirena.org.uk>
 <CAMuHMdUv8FFwkde8K3Ta8FEWrkkJ=9ZqbTi1EO8sRxVOhGtvzQ@mail.gmail.com>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha512;
        protocol="application/pgp-signature"; boundary="Pm+YXDPO8WF2t5nM"
Content-Disposition: inline
In-Reply-To: <CAMuHMdUv8FFwkde8K3Ta8FEWrkkJ=9ZqbTi1EO8sRxVOhGtvzQ@mail.gmail.com>
Precedence: bulk


--Pm+YXDPO8WF2t5nM
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

On Wed, Sep 27, 2023 at 11:10:58AM +0200, Geert Uytterhoeven wrote:
> On Wed, Sep 27, 2023 at 11:00=E2=80=AFAM Mark Brown <broonie@kernel.org> =
wrote:

> > The description is clearly saying there is a chip select, _NO_CS seems
> > entirely inappropriate.  It's not specified in the device tree because
> > when there's no chip select for a device it's a fundamental property of
> > how the device is controlled and we don't need any information beyond
> > the compatible.

> In host mode, it indeed doesn't matter, as you can have only a single
> device connected with SPI_NO_CS.
> In device mode, the device needs to know if it must monitor the chip
> select line or not.

> In hindsight, I should have kept the question I had written initially,
> but deleted after having read the documentation for the corresponding
> RZ/V2M register bits:

>     What does it mean if this is false? That there is no chip select?

> So "spi-no-cs" would be the inverse of "renesas,csi-ss".

I see.  Is there any control over what the chip select is when there is
one, in which case we could just look to see if there's one specified?

I'm a bit nervous about a generic property that maps onto _NO_CS since
it's likely that people will start using that in device bindings when
they shouldn't.

--Pm+YXDPO8WF2t5nM
Content-Type: application/pgp-signature; name="signature.asc"

-----BEGIN PGP SIGNATURE-----

iQEzBAABCgAdFiEEreZoqmdXGLWf4p/qJNaLcl1Uh9AFAmUT9DIACgkQJNaLcl1U
h9AoWgf8C4m4QGJxKqU2uTMR2OZGAiTjBvZPPRlWk3tOi86FMNdl2y3nyWSLo8Xn
wX09m6jOWe9hdlXxeP865u3KMrDvVsHaL8wF8T7jNQc4h7LwGdE2PxsjvWEXS9qL
301JwbJPnR0u3DMoCfv6QzfDsJdw3BWhMgjYsA5fid0cnOjY1BENubwtg5egP5qB
0XbxeqK6/6GGtLIVl4IVobJaJbt76H5jKvXrqUNVskKQg+FfxA2yE6aWRoAcGbVn
lQ09uL2W6G57XFRq9r4/R2y9AJWNgFeVmzpKsPSEiA/Yzd6RUHU/UN6mqAKNHgAi
VUZMiQi/SpBI7EqDkS/x22F4sENSAw==
=CrDz
-----END PGP SIGNATURE-----

--Pm+YXDPO8WF2t5nM--