GPIOIIC(4)

✨ GPIOIIC 💅

okay bestie, so this page is from the Kernel Interfaces Manual (section 4, the driver girlies) and it's literally all about gpioiic — the GPIO I2C bit-banging device driver. no cap. let's get into it 🦋

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🌸 NAME 🌸

gpioiic — GPIO I2C bit-banging device driver

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✨ SYNOPSIS ✨

so if you wanna compile this driver into the kernel, you gotta drop these lines into your kernel configuration file:

device gpio
device gpioiic
device iicbb
device iicbus

OR, if you'd rather load the driver as a module at boot time (lowkey easier), put this line in loader.conf(5):

gpioiic_load="YES"

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💖 DESCRIPTION 💖

The gpioiic driver gives you an IIC bit-banging interface using two GPIO pins — one for the SCL line and one for the SDA line on the bus. iconic behaviour, truly.

Here's the tea: gpioiic simulates an open collector kind of output when it's managing the pins on the bus — even on systems that don't directly support configuring gpio pins in that mode. The pins are never driven to the logical value of '1'. never ever. Instead they get driven to '0' or switched to input mode (Hi-Z/tri-state), and an external pullup resistor pulls the line to the 1 state unless some other device on the bus is driving it to 0. it's giving teamwork honestly 🤝

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🎀 HINTS CONFIGURATION 🎀

On a device.hints(5) based system, such as MIPS, these values are configurable for gpioiic:

• hint.gpioiic.%d.at — the gpiobus you are attaching to. Normally just gpiobus0 on systems with a single bank of gpio pins.
• hint.gpioiic.%d.pins — this is a bitmask of the pins on the gpiobus that are to be used for SCLOCK and SDATA from the GPIO IIC bit-banging bus. To configure pin 0 and 7, use the bitmask of 0b10000001 and convert it to a hexadecimal value of 0x0081. Please note that this mask should only ever have two bits set — any other bits (i.e., pins) will be ignored. And because gpioiic must be a child of the gpiobus, both gpio pins must be part of that bus. no exceptions bestie 🫶
• hint.gpioiic.%d.scl — indicates which bit in the hint.gpioiic.%d.pins should be used as the SCLOCK source. Optional, defaults to 0.
• hint.gpioiic.%d.sda — indicates which bit in the hint.gpioiic.%d.pins should be used as the SDATA source. Optional, defaults to 1.

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🦋 FDT CONFIGURATION 🦋

On an FDT(4) based system, such as ARM, the DTS node for gpioiic conforms to the standard bindings document i2c/i2c-gpio.yaml. The device node typically appears at the root of the device tree. Here's an example of a gpioiic node with one slave device on the IIC bus:

/ {
        gpioiic0 {
                compatible = "i2c-gpio";
                pinctrl-names = "default";
                pinctrl-0 = <&pinctrl_gpioiic0>;
                scl-gpios = <&gpio1  5 GPIO_ACTIVE_HIGH>;
                sda-gpios = <&gpio7 11 GPIO_ACTIVE_HIGH>;
                status = "okay";

                /* One slave device on the i2c bus. */
                rtc@51 {
                        compatible="nxp,pcf2127";
                        reg = <0x51>;
                        status = "okay";
                };
        };
};

Where:

• compatible — should be set to "i2c-gpio". The deprecated string "gpioiic" is also accepted for backwards compatibility. (yes she's old but she still works 💀)
• scl-gpios sda-gpios — these properties indicate which GPIO pins should be used for clock and data on the GPIO IIC bit-banging bus. There is no requirement that the two pins belong to the same gpio controller. go off, cross-controller queen 👑
• pinctrl-names pinctrl-0 — these properties may be required to configure the chosen pins as gpio pins, unless the pins default to that state on your system.

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👀 SEE ALSO 👀

fdt(4), gpio(4), iic(4), iicbb(4), iicbus(4)

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⭐ HISTORY ⭐

The gpioiic manual page first appeared in FreeBSD 10.1. a whole legend since day one, fr fr 🌈

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💜 AUTHORS 💜

This manual page was written by Luiz Otavio O Souza. king behaviour, we love to see it 🎀

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and that's the whole page bestie, you ate that 💅✨

anyway mwah, this one came from the Debian crew, dated December 1, 2019 — GPIOIIC(4) and out 🦋💖🌸