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Date: Wed, 15 Jan 2020 20:49:59 +0000
From: Chris Packham <Chris.Packham@...iedtelesis.co.nz>
To: "robh+dt@...nel.org" <robh+dt@...nel.org>
CC: "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
"mark.rutland@....com" <mark.rutland@....com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"broonie@...nel.org" <broonie@...nel.org>,
"anthony.derosa@...call7.com" <anthony.derosa@...call7.com>,
"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH 1/2] dt-bindings: spi: Document binding for generic SPI
multiplexer
Hi Rob,
On Wed, 2020-01-15 at 12:45 -0600, Rob Herring wrote:
> On Tue, Jan 14, 2020 at 5:39 PM Chris Packham
> <chris.packham@...iedtelesis.co.nz> wrote:
> >
> > Add binding documentation for the spi-mux driver. This allows a
> > generic
> > multiplexer to be used to provide access to multiple SPI devices.
> >
> > Signed-off-by: Chris Packham <chris.packham@...iedtelesis.co.nz>
> > ---
> > .../devicetree/bindings/spi/spi-mux.yaml | 82
> > +++++++++++++++++++
> > 1 file changed, 82 insertions(+)
> > create mode 100644 Documentation/devicetree/bindings/spi/spi-
> > mux.yaml
>
> Be sure to run 'make dt_binding_check'.
>
Will do.
> >
> > diff --git a/Documentation/devicetree/bindings/spi/spi-mux.yaml
> > b/Documentation/devicetree/bindings/spi/spi-mux.yaml
> > new file mode 100644
> > index 000000000000..1026d03a69c7
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/spi/spi-mux.yaml
> > @@ -0,0 +1,82 @@
> > +# SPDX-License-Identifier: GPL-2.0
>
> Dual license new bindings please:
>
> (GPL-2.0-only OR BSD-2-Clause)
>
Done
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/spi/spi-mux.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Generic SPI Multiplexer
> > +
> > +description: |
> > + This binding describes a SPI bus multiplexer to route the SPI
> > chip select
> > + signals. This can be used when you need more devices than the
> > SPI controller
> > + has chip selects available. An example setup is shown in ASCII
> > art; the actual
> > + setting of the multiplexer to a channel needs to be done by a
> > specific SPI mux
> > + driver.
> > +
> > + MOSI /--------------------------------+--------+--------+-
> > -------\
> > + MISO |/------------------------------+|-------+|-------+|-
> > ------\|
> > + SCL ||/----------------------------+||------+||------+||-
> > -----\||
> > + ||| ||| ||| |||
> > |||
> > + +----------
> > --+ ||| ||| ||| |||
> > + | SoC ||| | +-+++-+ +-+++-+ +-+++-
> > + +-+++-+
> > + | ||| | | dev | | dev | | dev
> > | | dev |
> > + | +--+++-+ | CS-X +------+\ +--+--+ +--+--+ +--+
> > --+ +--+--+
> > + | | SPI +-|-------+ Mux |\\ CS-0
> > | | | |
> > + | +------+ | +--+---+\\\-------/ CS-1
> > | | |
> > + | | | \\\----------------/ CS-2
> > | |
> > + | +------+ | | \\-------------------------
> > / CS-3 |
> > + | | ? +-|----------/ \--------------------------
> > --------/
> > + | +------+ |
> > + +------------+
> > +
> > +allOf:
> > + - $ref: "/schemas/spi/spi-controller.yaml#"
> > +
> > +properties:
> > + compatible:
> > + const: spi-mux
> > +
> > + mux-control:
> > + $ref: "/schemas/mux/mux-controller.yaml#"
>
> That file doesn't exist. If it did, it would still be wrong as that
> would be the provider side and this is the client.
>
> The correct name is also 'mux-controls'.
>
> You can assume it has a schema already and you just need to define
> how
> many entries it has (maxItems: 1).
I might need a little hand holding on this. Should I assume that there
is a separate schema for the consumer? Or leave out the $ref entirely?
> > +
> > +required:
> > + - compatible
> > + - reg
> > + - spi-max-frequency
> > + - mux-control
> > +
> > +examples:
> > + - |
> > + mux: mux-controller {
> > + compatible = "gpio-mux";
> > + #mux-control-cells = <0>;
> > +
> > + mux-gpios = <&gpio0 3 GPIO_ACTIVE_HIGH>;
> > + };
> > +
> > + spi {
> > + spi-mux {
>
> spi-mux@0
>
Done.
> > + compatible = "spi-mux";
> > + #address-cells = <1>;
> > + #size-cells = <0>;
> > + reg = <0>;
> > + spi-max-frequency = <100000000>;
>
> I don't think this makes sense here. The mux doesn't really have any
> frequency given the clock and data lines aren't routed thru the mux
> (though maybe that's possible if some isolation is needed).
>
It's needed to satisfy of_spi_parse_dt().To remove it I'd need to add
an escape hatch to allow this property to be omitted for spi-muxes. Or
change it to be a platform device and take the parent spi bus as a
phandle.
> > +
> > + mux-control = <&mux>
> > + mux-control-names = "spi";
>
> Not documented. Drop it as it's not all that useful when there's only
> 1 entry.
Done. Also updated mux-control -> mux-controls
> > +
> > + spi-flash@0 {
> > + compatible = "jedec,spi-nor";
> > + #address-cells = <1>;
> > + #size-cells = <1>;
> > + reg = <0>;
> > + spi-max-frequency = <40000000>;
> > + };
> > +
> > + spi-device@1 {
> > + compatible = "spidev";
>
> Not a valid compatible.
>
Picked a different one.
> > + reg = <1>;
> > + spi-max-frequency = <10000000>;
> > + };
> > + };
> > + };
> > --
> > 2.25.0
> >
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