| Message ID | 20190412050213.17698-2-chris.packham@alliedtelesis.co.nz |
|---|---|
| State | Changes Requested, archived |
| Headers | show |
| Series | spi: SPI bus multiplexer | expand |
| Context | Check | Description |
|---|---|---|
| robh/checkpatch | success |
On Fri, Apr 12, 2019 at 05:02:11PM +1200, Chris Packham wrote: > Add binding documentation for spi-mux-gpio which is a slightly more > complicated hardware implementation of using gpios to steer SPI chip > selects. > > Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz> > --- > .../devicetree/bindings/spi/spi-mux-gpio.txt | 45 +++++++++++++++++++ > 1 file changed, 45 insertions(+) > create mode 100644 Documentation/devicetree/bindings/spi/spi-mux-gpio.txt > > diff --git a/Documentation/devicetree/bindings/spi/spi-mux-gpio.txt b/Documentation/devicetree/bindings/spi/spi-mux-gpio.txt > new file mode 100644 > index 000000000000..a32f25321d37 > --- /dev/null > +++ b/Documentation/devicetree/bindings/spi/spi-mux-gpio.txt > @@ -0,0 +1,45 @@ > +SPI bus gpio multiplexer > + > +The SPI bus gpio multiplexer can be used to implement more complicated access > +logic than can be supported with the cs-gpios property of a SPI bus. > + > +In the example below we have a SoC with a single SPI CS that is gated by the > +state of a gpio to select the desired SPI device. > + > + +----------+ CS +-----+ CS0 +----+ > + | |--------| |------| | > + | | | \ / | +----+ > + | SoC | | + | > + | | GPIO | / \ | CS1 +----+ > + | |--------| |------| | > + +----------+ +-----+ +----+ > + > +Required properties: > +- compatible - must be "spi-mux-gpio" > +- gpios - gpios used to implement the multiplexing logic > +- spi-parent-bus - parent spi bus to use > + > +Optional properties: > +- spi-parent-cs - chip select on parent bus to use. Defaults to 0 if not > + specified. > + > +Example for a multiplexer with a single gpio: > + > + spi-mux { > + compatible = "spi-mux-gpio"; > + #address-cells = <1>; > + #size-cells = <0>; > + gpios = <&gpio0 1 0>; > + spi-parent-bus = <&spi0>; > + spi-parent-cs = <0>; Why is this out of band? We can do something similar to I2C and use the mux-control binding: spi { mux@0 { compatible = "spi-mux"; reg "0"; mux-controls = ...; spi-dev@0 {}; spi-dev@1 {}; }; spi-dev@1 {}; }; Rob
Hi Rob, On Mon, 2019-04-29 at 16:37 -0500, Rob Herring wrote: > On Fri, Apr 12, 2019 at 05:02:11PM +1200, Chris Packham wrote: > > Add binding documentation for spi-mux-gpio which is a slightly more > > complicated hardware implementation of using gpios to steer SPI chip > > selects. > > > > Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz> > > --- > > .../devicetree/bindings/spi/spi-mux-gpio.txt | 45 +++++++++++++++++++ > > 1 file changed, 45 insertions(+) > > create mode 100644 Documentation/devicetree/bindings/spi/spi-mux-gpio.txt > > > > diff --git a/Documentation/devicetree/bindings/spi/spi-mux-gpio.txt b/Documentation/devicetree/bindings/spi/spi-mux-gpio.txt > > new file mode 100644 > > index 000000000000..a32f25321d37 > > --- /dev/null > > +++ b/Documentation/devicetree/bindings/spi/spi-mux-gpio.txt > > @@ -0,0 +1,45 @@ > > +SPI bus gpio multiplexer > > + > > +The SPI bus gpio multiplexer can be used to implement more complicated access > > +logic than can be supported with the cs-gpios property of a SPI bus. > > + > > +In the example below we have a SoC with a single SPI CS that is gated by the > > +state of a gpio to select the desired SPI device. > > + > > + +----------+ CS +-----+ CS0 +----+ > > + | |--------| |------| | > > + | | | \ / | +----+ > > + | SoC | | + | > > + | | GPIO | / \ | CS1 +----+ > > + | |--------| |------| | > > + +----------+ +-----+ +----+ > > + > > +Required properties: > > +- compatible - must be "spi-mux-gpio" > > +- gpios - gpios used to implement the multiplexing logic > > +- spi-parent-bus - parent spi bus to use > > + > > +Optional properties: > > +- spi-parent-cs - chip select on parent bus to use. Defaults to 0 if not > > + specified. > > + > > +Example for a multiplexer with a single gpio: > > + > > + spi-mux { > > + compatible = "spi-mux-gpio"; > > + #address-cells = <1>; > > + #size-cells = <0>; > > + gpios = <&gpio0 1 0>; > > + spi-parent-bus = <&spi0>; > > + spi-parent-cs = <0>; > > Why is this out of band? We can do something similar to I2C and use the > mux-control binding: > > spi { > mux@0 { > compatible = "spi-mux"; > reg "0"; > mux-controls = ...; > > spi-dev@0 {}; > spi-dev@1 {}; > }; > > spi-dev@1 {}; > > }; I've been re-visiting this thread and an older one[1] with an eye on implementing a solution with mux-controls. One thing I'm confused about is your comment that the mux should be in- band like i2c. Looking at the one user of i2c-mux (at91-natte.dtsi) it also appears out of band and determine the parent bus with a i2c-parent property (similar to how I did it in my original submission). I also can't see how the mux would work in-band since it lacks the correct #address-cells etc for a spi device. I'm wondering if I've missed something obvious. -- [1] - https://patchwork.kernel.org/patch/2706151/
diff --git a/Documentation/devicetree/bindings/spi/spi-mux-gpio.txt b/Documentation/devicetree/bindings/spi/spi-mux-gpio.txt new file mode 100644 index 000000000000..a32f25321d37 --- /dev/null +++ b/Documentation/devicetree/bindings/spi/spi-mux-gpio.txt @@ -0,0 +1,45 @@ +SPI bus gpio multiplexer + +The SPI bus gpio multiplexer can be used to implement more complicated access +logic than can be supported with the cs-gpios property of a SPI bus. + +In the example below we have a SoC with a single SPI CS that is gated by the +state of a gpio to select the desired SPI device. + + +----------+ CS +-----+ CS0 +----+ + | |--------| |------| | + | | | \ / | +----+ + | SoC | | + | + | | GPIO | / \ | CS1 +----+ + | |--------| |------| | + +----------+ +-----+ +----+ + +Required properties: +- compatible - must be "spi-mux-gpio" +- gpios - gpios used to implement the multiplexing logic +- spi-parent-bus - parent spi bus to use + +Optional properties: +- spi-parent-cs - chip select on parent bus to use. Defaults to 0 if not + specified. + +Example for a multiplexer with a single gpio: + + spi-mux { + compatible = "spi-mux-gpio"; + #address-cells = <1>; + #size-cells = <0>; + gpios = <&gpio0 1 0>; + spi-parent-bus = <&spi0>; + spi-parent-cs = <0>; + + spi-dev@0 { + compatible = "..."; + reg = <0>; + } + + spi-dev@1 { + compatible = "..."; + reg = <1>; + } + };
Add binding documentation for spi-mux-gpio which is a slightly more complicated hardware implementation of using gpios to steer SPI chip selects. Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz> --- .../devicetree/bindings/spi/spi-mux-gpio.txt | 45 +++++++++++++++++++ 1 file changed, 45 insertions(+) create mode 100644 Documentation/devicetree/bindings/spi/spi-mux-gpio.txt