TDA2HG: How do we set a pin value in uboot or kernel?

Hi Terence,

For uboot:

You can go through code in this file : board/ti/am335x/board.c

Check gpio_request() and gpio_direction_output()

The gpio argument of gpio_request() is derived as follows : GPIO_TO_PIN(bank, bank_gpio)    (32 * (bank - 1) + (bank_gpio))

So in your case, it should be 

gpio_request(GPIO_TO_PIN(3,26), "my gpio");

For setting the GPIO high:

gpio_direction_output(GPIO_TO_PIN(3,26), 1);

For setting the GPIO low:

gpio_direction_output(GPIO_TO_PIN(3,26), 0);

For kernel:

Refer to these documents as starting point :    &  

1. pinmux would be set under "&am33xx_pinmux" field in the respective dts file. e.g: am335x-evm.dts. And pinmux phandle would be used by a device node. Say for example :

&mmc1 {
status = "okay";
vmmc-supply = <&vmmc_reg>;
bus-width = <4>;
pinctrl-names = "default";
pinctrl-0 = <&mmc1_pins>;
cd-gpios = <&gpio0 6 GPIO_ACTIVE_LOW>;
};

See mmc1_pins, under am335x_pinmux as below:

mmc1_pins: pinmux_mmc1_pins {
pinctrl-single,pins = <
AM33XX_IOPAD(0x960, PIN_INPUT | MUX_MODE7) /* spi0_cs1.gpio0_6 */
>;
};

And go through the code : drivers/mmc/host/omap_hsmmc.c, fubction omap_hsmmc_gpio_init(), specifically associated with "gpio_cd". You would come across devm_gpio APIs e.g. "devm_gpio_request_one" and gpiod_ APIs present in drivers/gpio/gpiolib.c and associate with above document

2. Second option in kernel is adding gpio-hog, where the GPIO driver itself will configure it to a specific value, if you do not want to change.