gpio: loongson: Create a dynamic platform device

It is pretty helpful to create some kind of device for backing the
GPIO chips, especially when preparing the driver for using
GENERIC_GPIO, so let's create a simple platform device and a simple
platform device driver and create the gpiochip in the .probe() routine
for the device driver. Keep all at the core initcall so the behaviour
is the same as before.

Cc: Keguang Zhang <keguang.zhang@gmail.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: Huacai Chen <chenhc@lemote.com>
Cc: linux-mips@linux-mips.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpio-loongson.c

@@ -18,6 +18,7 @@
 #include <linux/spinlock.h>
 #include <linux/err.h>
 #include <linux/gpio/driver.h>
+#include <linux/platform_device.h>
 #include <asm/types.h>
 #include <loongson.h>
 
@@ -97,19 +98,45 @@ static int loongson_gpio_direction_output(struct gpio_chip *chip,
 	return 0;
 }
 
-static struct gpio_chip loongson_chip = {
-	.label                  = "Loongson-gpio-chip",
-	.direction_input        = loongson_gpio_direction_input,
-	.get                    = loongson_gpio_get_value,
-	.direction_output       = loongson_gpio_direction_output,
-	.set                    = loongson_gpio_set_value,
-	.base			= 0,
-	.ngpio                  = LOONGSON_N_GPIO,
-	.can_sleep		= false,
+static int loongson_gpio_probe(struct platform_device *pdev)
+{
+	struct gpio_chip *gc;
+	struct device *dev = &pdev->dev;
+
+	gc = devm_kzalloc(dev, sizeof(*gc), GFP_KERNEL);
+	if (!gc)
+		return -ENOMEM;
+
+	gc->label = "loongson-gpio-chip";
+	gc->base = 0;
+	gc->ngpio = LOONGSON_N_GPIO;
+	gc->get = loongson_gpio_get_value;
+	gc->set = loongson_gpio_set_value;
+	gc->direction_input = loongson_gpio_direction_input;
+	gc->direction_output = loongson_gpio_direction_output;
+
+	return gpiochip_add_data(gc, NULL);
+}
+
+static struct platform_driver loongson_gpio_driver = {
+	.driver = {
+		.name = "loongson-gpio",
+	},
+	.probe = loongson_gpio_probe,
 };
 
 static int __init loongson_gpio_setup(void)
 {
-	return gpiochip_add_data(&loongson_chip, NULL);
+	struct platform_device *pdev;
+	int ret;
+
+	ret = platform_driver_register(&loongson_gpio_driver);
+	if (ret) {
+		pr_err("error registering loongson GPIO driver\n");
+		return ret;
+	}
+
+	pdev = platform_device_register_simple("loongson-gpio", -1, NULL, 0);
+	return PTR_ERR_OR_ZERO(pdev);
 }
 postcore_initcall(loongson_gpio_setup);