platform: introduce OF style 'modalias' support for platform bus

Fix a problem that, the platform bus supports the OF style modalias
in .uevent() call, but not in its device 'modalias' sysfs attribute.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/base/platform.c

@@ -679,6 +679,10 @@ static ssize_t modalias_show(struct device *dev, struct device_attribute *a,
 	struct platform_device	*pdev = to_platform_device(dev);
 	int len;
 
+	len = of_device_get_modalias(dev, buf, PAGE_SIZE -1);
+	if (len != -ENODEV)
+		return len;
+
 	len = acpi_device_modalias(dev, buf, PAGE_SIZE -1);
 	if (len != -ENODEV)
 		return len;

drivers/of/device.c

@@ -85,6 +85,9 @@ ssize_t of_device_get_modalias(struct device *dev, char *str, ssize_t len)
 	int cplen, i;
 	ssize_t tsize, csize, repend;
 
+	if ((!dev) || (!dev->of_node))
+		return -ENODEV;
+
 	/* Name & Type */
 	csize = snprintf(str, len, "of:N%sT%s", dev->of_node->name,
 			 dev->of_node->type);

include/linux/of_device.h

@@ -64,6 +64,12 @@ static inline int of_driver_match_device(struct device *dev,
 static inline void of_device_uevent(struct device *dev,
 			struct kobj_uevent_env *env) { }
 
+static inline int of_device_get_modalias(struct device *dev,
+				   char *str, ssize_t len)
+{
+	return -ENODEV;
+}
+
 static inline int of_device_uevent_modalias(struct device *dev,
 				   struct kobj_uevent_env *env)
 {