driver-core: platform: Provide helpers for multi-driver modules

Some modules register several sub-drivers. Provide a helper that makes
it easy to register and unregister a list of sub-drivers, as well as
unwind properly on error.

Signed-off-by: Thierry Reding <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/driver-model/platform.txt

···
 	int platform_driver_probe(struct platform_driver *drv,
 			  int (*probe)(struct platform_device *))
 
+Kernel modules can be composed of several platform drivers. The platform core
+provides helpers to register and unregister an array of drivers:
+
+	int __platform_register_drivers(struct platform_driver * const *drivers,
+				      unsigned int count, struct module *owner);
+	void platform_unregister_drivers(struct platform_driver * const *drivers,
+					 unsigned int count);
+
+If one of the drivers fails to register, all drivers registered up to that
+point will be unregistered in reverse order. Note that there is a convenience
+macro that passes THIS_MODULE as owner parameter:
+
+	#define platform_register_driver(drivers, count)
+
 
 Device Enumeration
 ~~~~~~~~~~~~~~~~~~

drivers/base/platform.c

···
 }
 EXPORT_SYMBOL_GPL(__platform_create_bundle);
 
+/**
+ * __platform_register_drivers - register an array of platform drivers
+ * @drivers: an array of drivers to register
+ * @count: the number of drivers to register
+ * @owner: module owning the drivers
+ *
+ * Registers platform drivers specified by an array. On failure to register a
+ * driver, all previously registered drivers will be unregistered. Callers of
+ * this API should use platform_unregister_drivers() to unregister drivers in
+ * the reverse order.
+ *
+ * Returns: 0 on success or a negative error code on failure.
+ */
+int __platform_register_drivers(struct platform_driver * const *drivers,
+				unsigned int count, struct module *owner)
+{
+	unsigned int i;
+	int err;
+
+	for (i = 0; i < count; i++) {
+		pr_debug("registering platform driver %ps\n", drivers[i]);
+
+		err = __platform_driver_register(drivers[i], owner);
+		if (err < 0) {
+			pr_err("failed to register platform driver %ps: %d\n",
+			       drivers[i], err);
+			goto error;
+		}
+	}
+
+	return 0;
+
+error:
+	while (i--) {
+		pr_debug("unregistering platform driver %ps\n", drivers[i]);
+		platform_driver_unregister(drivers[i]);
+	}
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(__platform_register_drivers);
+
+/**
+ * platform_unregister_drivers - unregister an array of platform drivers
+ * @drivers: an array of drivers to unregister
+ * @count: the number of drivers to unregister
+ *
+ * Unegisters platform drivers specified by an array. This is typically used
+ * to complement an earlier call to platform_register_drivers(). Drivers are
+ * unregistered in the reverse order in which they were registered.
+ */
+void platform_unregister_drivers(struct platform_driver * const *drivers,
+				 unsigned int count)
+{
+	while (count--) {
+		pr_debug("unregistering platform driver %ps\n", drivers[count]);
+		platform_driver_unregister(drivers[count]);
+	}
+}
+EXPORT_SYMBOL_GPL(platform_unregister_drivers);
+
 /* modalias support enables more hands-off userspace setup:
  * (a) environment variable lets new-style hotplug events work once system is
  *     fully running:  "modprobe $MODALIAS"

include/linux/platform_device.h

···
 	struct resource *res, unsigned int n_res,
 	const void *data, size_t size, struct module *module);
 
+int __platform_register_drivers(struct platform_driver * const *drivers,
+				unsigned int count, struct module *owner);
+void platform_unregister_drivers(struct platform_driver * const *drivers,
+				 unsigned int count);
+
+#define platform_register_drivers(drivers, count) \
+	__platform_register_drivers(drivers, count, THIS_MODULE)
+
 /* early platform driver interface */
 struct early_platform_driver {
 	const char *class_str;