Uncover the secret of the undocumented trick in `gpio_set_level()` when initializing the display.

[SinglWolf]

For a long time I did not want to update the drivers for my project, but I did it anyway.
While looking at the innovations, I noticed something new for me.
Explain to me, please, how this can be?
The function from the esp-idf framework only accepts the following arguments:

/**
 * @brief  GPIO set output level
 *
 * @param  gpio_num GPIO number. If you want to set the output level of e.g. GPIO16, gpio_num should be GPIO_NUM_16 (16);
 * @param  level Output level. 0: low ; 1: high
 *
 * @return
 *     - ESP_OK Success
 *     - ESP_ERR_INVALID_ARG GPIO number error
 *
 */
esp_err_t gpio_set_level(gpio_num_t gpio_num, uint32_t level);

With gpio_num, everything me is clear, but with level there is some misunderstanding.
Watch the headline briefing, it says:

 * @param  level Output level. 0: low ; 1: high

Now let's turn to the disp_backlight_set() function:

void disp_backlight_set(disp_backlight_h bckl, int brightness_percent)
{
    // Check input paramters
    if (bckl == NULL)
        return;
    if (brightness_percent > 100)
        brightness_percent = 100;
    if (brightness_percent < 0)
        brightness_percent = 0;

    disp_backlight_t *bckl_dev = (disp_backlight_t *) bckl;
    ESP_LOGI(TAG, "Setting LCD backlight: %d%%", brightness_percent);

    if (bckl_dev->pwm_control) {
        uint32_t duty_cycle = (1023 * brightness_percent) / 100; // LEDC resolution set to 10bits, thus: 100% = 1023
        ESP_ERROR_CHECK(ledc_set_duty(LEDC_LOW_SPEED_MODE, bckl_dev->index, duty_cycle));
        ESP_ERROR_CHECK(ledc_update_duty(LEDC_LOW_SPEED_MODE, bckl_dev->index));
    } else {
        ESP_ERROR_CHECK(gpio_set_level(bckl_dev->index, brightness_percent));
    }
}

This function is called when the display is initialized as follows:

disp_backlight_set(bckl_handle, 100);

As a result, the function gpio_set_level() receives a argument level equal to 100.
Uncover the secret of the undocumented trick in gpio_set_level() when initializing the display.
P.S. Setting Kconfig: Backlight Control (Switch control)
Point menu [*] Is backlight turn on with a HIGH (1) logic level? or [*] Is backlight turn on with a HIGH (0) logic level? does not affect anything.

[C47D]

Hi,

If you follow what's inside the gpio_set_level you end up in gpio_ll_set_level, you can see the implementation here, basically it only checks if level is 0 or not 0, so if level is 1 or 100 it ends up being the same.

We should update the docs with this comment, thanks for reporting it.