Can I run 2 device tree overlay at the same time?

Question

I'm trying to monitor some 4-20mA current loops and 0-10V generators with a RPi 3. I found these modules which would do the job:

https://widgetlords.com/products/pi-spi-2a0-raspberry-pi-analog-output-ma-vdc-interface for the 0-10V and 4-20mA generator

https://widgetlords.com/collections/pi-spi-din-series/products/raspberry-pi-din-rail-analog-input-interface for the inputs.

The problem is that both devices use different libraries, and these libraries use different 'dtoverlays'. They say on the web site to activate in the '/boot/config.txt'

dtoverlay = pi-spi for the output device

dtoverlay = vpe-2701c for the input device

I put the code of the overlays down

I don't know if I can uncomment both lines at the same time so I can run a script that takes input and generates outputs ...

I took a look on the net but the device trees are quiet difficult to understand for me.

Would it be a problem to have 2 device tree overlays used by the same script ?

pi-spi overlay:

/dts-v1/;
/plugin/;

/ {
    compatible = "brcm,bcm2835", "brcm,bcm2836", "brcm,bcm2708", "brcm,bcm2709";

    fragment@0 {
        target = <&spi0>;
        frag0: __overlay__ {
            #address-cells = <1>;
            #size-cells = <0>;
            pinctrl-0 = <&spi0_pins &spi0_cs_pins>;
            status = "okay";
            cs-gpios = <&gpio 8 1>,     /* 8KO */ 
                   <&gpio 7 1>,     /* 8AI */
                   <&gpio 4 1>,     /* 2AO */
                   <&gpio 17 1>,    /* 8DI */
                   <&gpio 22 1>;    /* SPARE */

            spidev@2{
                compatible = "spidev";
                reg = <2>;  /* CE2 */
                #address-cells = <1>;
                #size-cells = <0>;
                spi-max-frequency = <1000000>;
            };

            spidev@3{
                compatible = "spidev";
                reg = <3>;  /* CE3 */
                #address-cells = <1>;
                #size-cells = <0>;
                spi-max-frequency = <1000000>;
            };

            spidev@4{
                compatible = "spidev";
                reg = <4>;  /* CE4 */
                #address-cells = <1>;
                #size-cells = <0>;
                spi-max-frequency = <1000000>;
            };

        };
    };

    fragment@1 {
        target = <&spi0_cs_pins>;
        frag1: __overlay__ {
            brcm,pins = <8 7 4 17 22>;
            brcm,function = <1>; /* out */
        };
    };
};

vpe-2701c overlay:

/dts-v1/;
/plugin/;

/ {
    compatible = "brcm,bcm2835", "brcm,bcm2836", "brcm,bcm2708", "brcm,bcm2709";

    fragment@0 {
        target = <&spi0>;
        frag0: __overlay__ {
            #address-cells = <1>;
            #size-cells = <0>;
            pinctrl-0 = <&spi0_pins &spi0_cs_pins>;
            status = "okay";
            cs-gpios = <&gpio 8 1>,     /* CE0 */ 
                   <&gpio 7 1>,     /* CE1 */
                   <&gpio 24 1>,    /* CE2 */
                   <&gpio 23 1>,    /* CE3 */
                   <&gpio 18 1>;    /* CE4 */

            spidev@2{
                compatible = "spidev";
                reg = <2>;  /* CE2 */
                #address-cells = <1>;
                #size-cells = <0>;
                spi-max-frequency = <1000000>;
            };

            spidev@3{
                compatible = "spidev";
                reg = <3>;  /* CE3 */
                #address-cells = <1>;
                #size-cells = <0>;
                spi-max-frequency = <1000000>;
            };

            spidev@4{
                compatible = "spidev";
                reg = <4>;  /* CE4 */
                #address-cells = <1>;
                #size-cells = <0>;
                spi-max-frequency = <1000000>;
            };

        };
    };

    fragment@1 {
        target = <&spi0_cs_pins>;
        frag1: __overlay__ {
            brcm,pins = <8 7 18 23 24>;
            brcm,function = <1>; /* out */
        };
    };

    fragment@2 {
        target = <&i2c_arm>;
        __overlay__ {
            #address-cells = <1>;
            #size-cells = <0>;
            status = "okay";

            mcp7941x: mcp7941x@6f {
                compatible = "microchip,mcp7941x";
                reg = <0x6f>;
                status = "okay";
            };
        };
    };
};

Answer 1

You are NOT using "different 'dtoverlays'".

Libraries do NOT "use … 'dtoverlays'" they may use resources initialised by overlays.

Device Tree is a mechanism for configuring the hardware and modules which are loaded - more specifically for modifying the default settings by the default dtb.

I typically include ~6 in my configuration.

Provided the dtoverlays do not use the same resource there is no issue, although it appears these are both attempting to use the SPI interface.

The Pi has 2 SPI interfaces, so it may be possible to use both - with software changes.

The "documentation" linked is inconsistent, but a superficial reading indicates both use MOSI, MISO, SCLK (but different CE pins). SPI can be shared - this is normally mediated by CE pins and the kernel module supports 2 CE pins, but it is possible to use as many CE pins as desired, if the software is written to support this.