gpio: make the gpiochip a real device

GPIO chips have been around for years, but were never real devices,
instead they were piggy-backing on a parent device (such as a
platform_device or amba_device) but this was always optional.
GPIO chips could also exist without any device at all, with its
struct device *parent (ex *dev) pointer being set to null.

When sysfs was in use, a mock device would be created, with the
optional parent assigned, or just floating orphaned with NULL
as parent.

If sysfs is active, it will use this device as parent.

We now create a gpio_device struct containing a real
struct device and move the subsystem over to using that. The
list of struct gpio_chip:s is augmented to hold struct
gpio_device:s and we find gpio_chips:s by first looking up
the struct gpio_device.

The struct gpio_device is designed to stay around even if the
gpio_chip is removed, so as to satisfy users in userspace
that need a backing data structure to hold the state of the
session initiated with e.g. a character device even if there is
no physical chip anymore.

From this point on, gpiochips are devices.

Cc: Johan Hovold <johan@kernel.org>
Cc: Michael Welling <mwelling@ieee.org>
Cc: Markus Pargmann <mpa@pengutronix.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpiolib-sysfs.c

@@ -547,6 +547,7 @@ static struct class gpio_class = {
 int gpiod_export(struct gpio_desc *desc, bool direction_may_change)
 {
 	struct gpio_chip	*chip;
+	struct gpio_device	*gdev;
 	struct gpiod_data	*data;
 	unsigned long		flags;
 	int			status;
@@ -566,6 +567,7 @@ int gpiod_export(struct gpio_desc *desc, bool direction_may_change)
 	}
 
 	chip = desc->chip;
+	gdev = chip->gpiodev;
 
 	mutex_lock(&sysfs_lock);
 
@@ -605,7 +607,7 @@ int gpiod_export(struct gpio_desc *desc, bool direction_may_change)
 	if (chip->names && chip->names[offset])
 		ioname = chip->names[offset];
 
-	dev = device_create_with_groups(&gpio_class, chip->parent,
+	dev = device_create_with_groups(&gpio_class, &gdev->dev,
 					MKDEV(0, 0), data, gpio_groups,
 					ioname ? ioname : "gpio%u",
 					desc_to_gpio(desc));
@@ -771,7 +773,7 @@ static int __init gpiolib_sysfs_init(void)
 {
 	int		status;
 	unsigned long	flags;
-	struct gpio_chip *chip;
+	struct gpio_device *gdev;
 
 	status = class_register(&gpio_class);
 	if (status < 0)
@@ -784,8 +786,8 @@ static int __init gpiolib_sysfs_init(void)
 	 * registered, and so arch_initcall() can always gpio_export().
 	 */
 	spin_lock_irqsave(&gpio_lock, flags);
-	list_for_each_entry(chip, &gpio_chips, list) {
-		if (chip->cdev)
+	list_for_each_entry(gdev, &gpio_devices, list) {
+		if (gdev->chip->cdev)
 			continue;
 
 		/*
@@ -798,7 +800,7 @@ static int __init gpiolib_sysfs_init(void)
 		 * gpio_lock prevents us from doing this.
 		 */
 		spin_unlock_irqrestore(&gpio_lock, flags);
-		status = gpiochip_sysfs_register(chip);
+		status = gpiochip_sysfs_register(gdev->chip);
 		spin_lock_irqsave(&gpio_lock, flags);
 	}
 	spin_unlock_irqrestore(&gpio_lock, flags);