WhyCan Forum(哇酷开发者社区)

static int fbtft_request_one_gpio(struct fbtft_par *par,
				  const char *name, int index,
				  struct gpio_desc **gpiop)
{
	struct device *dev = par->info->device;

	*gpiop = devm_gpiod_get_index_optional(dev, name, index,
					       GPIOD_OUT_LOW);
	if (IS_ERR(*gpiop))
		return dev_err_probe(dev, PTR_ERR(*gpiop), "Failed to request %s GPIO\n", name);

	fbtft_par_dbg(DEBUG_REQUEST_GPIOS, par, "%s: '%s' GPIO\n",
		      __func__, name);

	return 0;
}

static int fbtft_request_one_gpio(struct fbtft_par *par,
				  const char *name, int index,
				  struct gpio_desc **gpiop)
{
    struct device *dev = par->info->device;
    struct device_node *node = dev->of_node;
    int gpio, flags, ret = 0;
    enum of_gpio_flags of_flags;
	char gpio_names[32];

	sprintf(gpio_names, "%s-gpios", name);
    if (of_find_property(node, gpio_names, NULL)) {
        gpio = of_get_named_gpio_flags(node, gpio_names, index, &of_flags);
        if (gpio == -ENOENT)
            return 0;
        if (gpio == -EPROBE_DEFER)
            return gpio;
        if (gpio < 0) {
            dev_err(dev,
                "failed to get '%s' from DT\n", gpio_names);
            return gpio;
        }

         //active low translates to initially low 
        flags = (of_flags & OF_GPIO_ACTIVE_LOW) ? GPIOF_OUT_INIT_LOW :
                            GPIOF_OUT_INIT_HIGH;
        ret = devm_gpio_request_one(dev, gpio, flags,
                        dev->driver->name);
        if (ret) {
            dev_err(dev,
                "gpio_request_one('%s'=%d) failed with %d\n",
                gpio_names, gpio, ret);
            return ret;
        }

        *gpiop = gpio_to_desc(gpio);
        fbtft_par_dbg(DEBUG_REQUEST_GPIOS, par, "%s: '%s' = GPIO%d\n",
                            __func__, gpio_names, gpio);
    }
    return ret;
}