[PATCH] platform_bus learns about modalias

This patch adds modalias support to platform devices, for simpler
hotplug/coldplug driven driver setup.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/base/platform.c

@@ -452,6 +452,37 @@ void platform_driver_unregister(struct platform_driver *drv)
 EXPORT_SYMBOL_GPL(platform_driver_unregister);
 
 
+/* modalias support enables more hands-off userspace setup:
+ * (a) environment variable lets new-style hotplug events work once system is
+ *     fully running:  "modprobe $MODALIAS"
+ * (b) sysfs attribute lets new-style coldplug recover from hotplug events
+ *     mishandled before system is fully running:  "modprobe $(cat modalias)"
+ */
+static ssize_t
+modalias_show(struct device *dev, struct device_attribute *a, char *buf)
+{
+	struct platform_device	*pdev = to_platform_device(dev);
+	int len = snprintf(buf, PAGE_SIZE, "%s\n", pdev->name);
+
+	return (len >= PAGE_SIZE) ? (PAGE_SIZE - 1) : len;
+}
+
+static struct device_attribute platform_dev_attrs[] = {
+	__ATTR_RO(modalias),
+	__ATTR_NULL,
+};
+
+static int platform_uevent(struct device *dev, char **envp, int num_envp,
+		char *buffer, int buffer_size)
+{
+	struct platform_device	*pdev = to_platform_device(dev);
+
+	envp[0] = buffer;
+	snprintf(buffer, buffer_size, "MODALIAS=%s", pdev->name);
+	return 0;
+}
+
+
 /**
  *	platform_match - bind platform device to platform driver.
  *	@dev:	device.
@@ -496,7 +527,9 @@ static int platform_resume(struct device * dev)
 
 struct bus_type platform_bus_type = {
 	.name		= "platform",
+	.dev_attrs	= platform_dev_attrs,
 	.match		= platform_match,
+	.uevent		= platform_uevent,
 	.suspend	= platform_suspend,
 	.resume		= platform_resume,
 };