Date: Tue, 18 Apr 2017 12:34:53 +0200
From: Pavel Machek <pavel@ucw.cz>
To: Sakari Ailus <sakari.ailus@iki.fi>
Cc: Philipp Zabel <p.zabel@pengutronix.de>, Peter Rosin <peda@axentia.se>,
        Rob Herring <robh+dt@kernel.org>, Mark Rutland <mark.rutland@arm.com>,
        Steve Longerbeam <slongerbeam@gmail.com>, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, kernel@pengutronix.de
Subject: Re: [RFC 1/2] dt-bindings: add mmio-based syscon mux controller DT
 bindings
Message-ID: <20170418103453.GC14505@amd>
References: <20170413154812.19597-1-p.zabel@pengutronix.de>
 <1492503544.2432.32.camel@pengutronix.de>
 <20170418100840.GF7456@valkosipuli.retiisi.org.uk>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha1;
        protocol="application/pgp-signature"; boundary="ABTtc+pdwF7KHXCz"
Content-Disposition: inline
In-Reply-To: <20170418100840.GF7456@valkosipuli.retiisi.org.uk>
User-Agent: Mutt/1.5.23 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 3761
Lines: 122


--ABTtc+pdwF7KHXCz
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

On Tue 2017-04-18 13:08:41, Sakari Ailus wrote:
> Hi Philipp,
>=20
> On Tue, Apr 18, 2017 at 10:19:04AM +0200, Philipp Zabel wrote:
> > On Thu, 2017-04-13 at 17:48 +0200, Philipp Zabel wrote:
> > > This adds device tree binding documentation for mmio-based syscon
> > > multiplexers controlled by a single bitfield in a syscon register
> > > range.
> > >=20
> > > Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
> > > ---
> > >  Documentation/devicetree/bindings/mux/mmio-mux.txt | 56 ++++++++++++=
++++++++++
> > >  1 file changed, 56 insertions(+)
> > >  create mode 100644 Documentation/devicetree/bindings/mux/mmio-mux.txt
> > >=20
> > > diff --git a/Documentation/devicetree/bindings/mux/mmio-mux.txt b/Doc=
umentation/devicetree/bindings/mux/mmio-mux.txt
> > > new file mode 100644
> > > index 0000000000000..11d96f5d98583
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/mux/mmio-mux.txt
> > > @@ -0,0 +1,56 @@
> > > +MMIO bitfield-based multiplexer controller bindings
> > > +
> > > +Define a syscon bitfield to be used to control a multiplexer. The pa=
rent
> > > +device tree node must be a syscon node to provide register access.
> > > +
> > > +Required properties:
> > > +- compatible : "gpio-mux"
> > > +- reg : register base of the register containing the control bitfield
> > > +- bit-mask : bitmask of the control bitfield in the control register
> > > +- bit-shift : bit offset of the control bitfield in the control regi=
ster
> > > +- #mux-control-cells : <0>
> > > +* Standard mux-controller bindings as decribed in mux-controller.txt
> > > +
> > > +Optional properties:
> > > +- idle-state : if present, the state the mux will have when idle. The
> > > +	       special state MUX_IDLE_AS_IS is the default.
> > > +
> > > +The multiplexer state is defined as the value of the bitfield descri=
bed
> > > +by the reg, bit-mask, and bit-shift properties, accessed through the=
 parent
> > > +syscon.
> > > +
> > > +Example:
> > > +
> > > +	syscon {
> > > +		compatible =3D "syscon";
> > > +
> > > +		mux: mux-controller@3 {
> > > +			compatible =3D "mmio-mux";
> > > +			reg =3D <0x3>;
> > > +			bit-mask =3D <0x1>;
> > > +			bit-shift =3D <5>;
> > > +			#mux-control-cells =3D <0>;
> > > +		};
> > > +	};
> > > +
> > > +	video-mux {
> > > +		compatible =3D "video-mux";
> > > +		mux-controls =3D <&mux>;
> > > +
> > > +		ports {
> > > +			/* input 0 */
> > > +			port@0 {
> > > +				reg =3D <0>;
> > > +			};
> > > +
> > > +			/* input 1 */
> > > +			port@1 {
> > > +				reg =3D <1>;
> > > +			};
> > > +
> > > +			/* output */
> > > +			port@2 {
> > > +				reg =3D <2>;
> > > +			};
> > > +		};
> > > +	};
> >=20
> > So Pavel (added to Cc:) suggested to merge these into one node for the
> > video mux, as really we are describing a single hardware entity that
> > happens to be multiplexing multiple video buses into one:
>=20
> Two drivers will be needed in a way or another to disconnect the dependen=
cy
> between the video switch driver and the MUX implementation. Are there ways
> to do that cleanly other than having two devices?

Yes.

Device tree describes hardware, not the driver structure.

									Pavel
--=20
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blo=
g.html

--ABTtc+pdwF7KHXCz
Content-Type: application/pgp-signature; name="signature.asc"
Content-Description: Digital signature

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1

iEYEARECAAYFAlj1680ACgkQMOfwapXb+vKIwQCfQa0NhkUw7ttvjv8W6933LhvT
QegAoK40QkezTBWUuN5oM6/3jh029HcS
=Spyn
-----END PGP SIGNATURE-----

--ABTtc+pdwF7KHXCz--