Re: [PATCH 1/2] dt-bindings: spi: Document binding for generic SPI multiplexer

[Chris Packham]

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@xxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxx>
> > ---
> >  .../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
> >