Device Tree Overlay to name GPIO lines on a Raspberry Pi 2 Model B. Needed for Kernels < 5.2

gpio-pinnames.dts

// Give GPIO pin names in pre-5.2 kernels
/dts-v1/;
/plugin/;

/ {
    compatible = "raspberrypi,2-model-b", "brcm,bcm2836";
    fragment@0 {
      target = <&gpio>;
      __overlay__ {
	/*
	 * Taken from rpi_SCH_2b_1p2_reduced.pdf and
	 * the official GPU firmware DT blob.
	 *
	 * Legend:
	 * "NC" = not connected (no rail from the SoC)
	 * "FOO" = GPIO line named "FOO" on the schematic
	 * "FOO_N" = GPIO line named "FOO" on schematic, active low
	 */
	gpio-line-names = "ID_SDA",
			  "ID_SCL",
			  "SDA1",
			  "SCL1",
			  "GPIO_GCLK",
			  "GPIO5",
			  "GPIO6",
			  "SPI_CE1_N",
			  "SPI_CE0_N",
			  "SPI_MISO",
			  "SPI_MOSI",
			  "SPI_SCLK",
			  "GPIO12",
			  "GPIO13",
			  /* Serial port */
			  "TXD0",
			  "RXD0",
			  "GPIO16",
			  "GPIO17",
			  "GPIO18",
			  "GPIO19",
			  "GPIO20",
			  "GPIO21",
			  "GPIO22",
			  "GPIO23",
			  "GPIO24",
			  "GPIO25",
			  "GPIO26",
			  "GPIO27",
			  "SDA0",
			  "SCL0",
			  "", /* GPIO30 */
			  "LAN_RUN",
			  "CAM_GPIO1",
			  "", /* GPIO33 */
			  "", /* GPIO34 */
			  "PWR_LOW_N",
			  "", /* GPIO36 */
			  "", /* GPIO37 */
			  "USB_LIMIT",
			  "", /* GPIO39 */
			  "PWM0_OUT",
			  "CAM_GPIO0",
			  "SMPS_SCL",
			  "SMPS_SDA",
			  "ETHCLK",
			  "PWM1_OUT",
			  "HDMI_HPD_N",
			  "STATUS_LED",
			  /* Used by SD Card */
			  "SD_CLK_R",
			  "SD_CMD_R",
			  "SD_DATA0_R",
			  "SD_DATA1_R",
			  "SD_DATA2_R",
			  "SD_DATA3_R";
      };
    };
};