Add ability to export gpio used by gpio-poweroff

raspberrypi inclusion
category: feature
bugzilla: 50432

--------------------------------
Signed-off-by: NNick Bulleid <nedbulleid@fastmail.com>

Added export feature to gpio-poweroff documentation
Signed-off-by: NNick Bulleid <nedbulleid@fastmail.com>
Signed-off-by: NFang Yafen <yafen@iscas.ac.cn>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

Documentation/devicetree/bindings/power/reset/gpio-poweroff.txt

@@ -31,6 +31,7 @@ Optional properties:
 - inactive-delay-ms: Delay (default 100) to wait after driving gpio inactive
 - timeout-ms: Time to wait before asserting a WARN_ON(1). If nothing is
               specified, 3000 ms is used.
+- export : Export the GPIO line to the sysfs system
 
 Examples:
 

drivers/power/reset/gpio-poweroff.c

@@ -51,6 +51,7 @@ static int gpio_poweroff_probe(struct platform_device *pdev)
 	bool input = false;
 	enum gpiod_flags flags;
 	bool force = false;
+	bool export = false;
 
 	/* If a pm_power_off function has already been added, leave it alone */
 	force = of_property_read_bool(pdev->dev.of_node, "force");
@@ -76,6 +77,12 @@ static int gpio_poweroff_probe(struct platform_device *pdev)
 	if (IS_ERR(reset_gpio))
 		return PTR_ERR(reset_gpio);
 
+	export = of_property_read_bool(pdev->dev.of_node, "export");
+	if (export) {
+		gpiod_export(reset_gpio, false);
+		gpiod_export_link(&pdev->dev, "poweroff-gpio", reset_gpio);
+	}
+
 	pm_power_off = &gpio_poweroff_do_poweroff;
 	return 0;
 }
@@ -85,6 +92,8 @@ static int gpio_poweroff_remove(struct platform_device *pdev)
 	if (pm_power_off == &gpio_poweroff_do_poweroff)
 		pm_power_off = NULL;
 
+	gpiod_unexport(reset_gpio);
+
 	return 0;
 }