u-boot/doc/device-tree-bindings/spi/soft-spi.txt
Miquel Raynal 32466c445c doc: bindings: soft-spi: update documentation to match the code
Linux bindings have been introduced in the code (removing the U-Boot
specific ones) without documentation update. Compatible string has
changed, as well as the four GPIO properties. Reflect this by updating
the soft-spi.txt documentation.

Fixes: 102412c415 ("dm: spi: soft_spi: switch to use linux compatible string")
Signed-off-by: Miquel Raynal <miquel.raynal@free-electrons.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>
2018-01-10 12:06:15 +05:30

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Soft SPI
The soft SPI bus implementation allows the use of GPIO pins to simulate a
SPI bus. No SPI host is required for this to work. The down-side is that the
performance will typically be much lower than a real SPI bus.
The soft SPI node requires the following properties:
Mandatory properties:
compatible: "spi-gpio"
cs-gpios: GPIOs to use for SPI chip select (output)
gpio-sck: GPIO to use for SPI clock (output)
And at least one of:
gpio-mosi: GPIO to use for SPI MOSI line (output)
gpio-miso: GPIO to use for SPI MISO line (input)
Optional propertie:
spi-delay-us: Number of microseconds of delay between each CS transition
The GPIOs should be specified as required by the GPIO controller referenced.
The first cell holds the phandle of the controller and the second cell
typically holds the GPIO number.
Example:
soft-spi {
compatible = "spi-gpio";
cs-gpios = <&gpio 235 0>; /* Y43 */
gpio-sck = <&gpio 225 0>; /* Y31 */
gpio-mosi = <&gpio 227 0>; /* Y33 */
gpio-miso = <&gpio 224 0>; /* Y30 */
spi-delay-us = <1>;
#address-cells = <1>;
#size-cells = <0>;
cs@0 {
};
};