Devicetree overlay

/dts-v1/;
/plugin/;

/ {
    	compatible = "ti,beaglebone", "ti,beaglebone-black";

	/* identification */
    	part-number = "tlc5946_gpio_pins";

    	fragment@0 {
        	target = <&am33xx_pinmux>;
        	__overlay__ {
            		pinctrl_tlc5946: pinctrl_tlc5946_pins {
                	pinctrl-single,pins = <
                 		0x074 0x37 /* xerr:  P9_13 = uart4_txd, INPUT_PULLUP  | MODE7 */
                 		0x040 0x17 /* mode:  P9_15 = gpio1_16,  OUTPUT_PULLUP | MODE7 */
                 		0x04c 0x17 /* blank: P9_16 = ehrpwm1b,  OUTPUT_PULLUP | MODE7 */
                 		0x044 0x17 /* xhalf: P9_23 = gpio1_17,  OUTPUT_PULLUP | MODE7 */
             			>;
            		};
        	};
    	};

	fragment@1 {
		target = <&ocp>;
		__overlay__ {
			#address-cells = <1>;
			#size-cells = <1>;
			tlc_gpios {
				compatible = "bone-pinmux-helper";
				pinctrl-names = "default";
				pinctrl-0 = <&pinctrl_tlc5946>;
				status = "okay";
			};
		};
	};

};

Test application flipping all bits in GPIO1 output register

#include <stdio.h>
#include <fcntl.h>
#include <sys/mman.h>

#define DATA_OUT_REG 0x13C
static void test_gpio()
{
        int gpio_fd = open("/dev/mem", O_RDWR | O_SYNC);
        if (gpio_fd < 0)
        {
                printf("Cannot open /dev/mem\n");
                return;
        }

        unsigned long *gpio = (unsigned long *) mmap(NULL, 0xFFF,
                        PROT_READ | PROT_WRITE, MAP_SHARED, gpio_fd, 0x4804C000);
        if (gpio <= 0)
        {
                printf("GPIO Mapping failed\n");
                return;
        }

        unsigned int i=0;
        for(;;)
        {
                printf("Loop %i, setting 0\n",i);
                gpio[DATA_OUT_REG / 4]=0;
                sleep(1);
                printf("Loop %i, setting 1\n",i);
                gpio[DATA_OUT_REG / 4]=0xffffffff;
                sleep(1);
                i++;
        }

}

int main()
{
        test_gpio();
        return 0;
}