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mcbridejc/Adding SPI chip selects on Raspberry Pi.md

Last active November 11, 2025 09:33
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How to add or change SPI chip select pins on raspberry PI with device tree overlay
Raw
Adding SPI chip selects on Raspberry Pi.md

The raspberry pi SPI0 by default has 2 CS pins configured. The SPI driver in the kernel uses GPIOS toggled by software, rather than hardware controlled chip selects. This means that any GPIO can be used for a chip select, and any number of them can be supported concurrently. All of these setup for the SPI driver is defined in the device tree, and we can use device tree overlays stored in /boot to dynamically configure the device tree.

The attached example creates a SPI device with 5 CS pins, on GPIO 8, 7, 1, 5, and 6.

To compile it to a binary: dtc -@ -I dts -O dtb -o spi-cs-extend.dtbo spi-cs-extend.dts

Then place spi-cs-extend.dtbo into /boot/overlays and add the following line to your /boot/config.txt: dtoverlay=spi-cs-extend.

After your next reboot, you should find /dev/spi0.2, /dev/spi0.3, and /dev/spi0.4 have been created.

Raw
spi-cs-extend.dts
/dts-v1/;
/plugin/;
/ {
compatible = "brcm,bcm2835";
fragment@0 {
target = <&spi0_cs_pins>;
frag0: __overlay__ {
brcm,pins = <8 7 1 5 6>;
};
};
fragment@1 {
target = <&spi0>;
frag1: __overlay__ {
#address-cells = <1>;
#size-cells = <0>;
cs-gpios = <&gpio 8 1>, <&gpio 7 1>, <&gpio 1 1>, <&gpio 5 1>, <&gpio 6 1>;
status = "okay";
spidev0_2: spidev@2 {
compatible = "spidev";
reg = <2>;
#address-cells = <1>;
#size-cells = <0>;
spi-max-frequency = <125000000>;
};
spidev0_3: spidev@3 {
compatible = "spidev";
reg = <3>;
#address-cells = <1>;
#size-cells = <0>;
spi-max-frequency = <125000000>;
};
spidev0_4: spidev@4 {
compatible = "spidev";
reg = <4>;
#address-cells = <1>;
#size-cells = <0>;
spi-max-frequency = <125000000>;
};
};
};
};
@irgendwienet
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irgendwienet commented Mar 1, 2025

If you want to use high-active CS pins instead of low-active (the default) you can add spi-cs-high; for some or all devices:

                        spidev0_2: spidev@2 {
                                compatible = "spidev";
                                reg = <2>;
                                #address-cells = <1>;
                                #size-cells = <0>;
                                spi-max-frequency = <125000000>;
                                spi-cs-high;
                        };

To test or debug this the gpioinfo tool is very usefull.

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