rpmsg: Make modalias work for DeviceTree based devices

When rpmsg devices are expected to be matched based on their compatible
the modalias should reflect this, so that module autoloading has a
chance to match and load the appropriate module.
Tested-by: Rob Clark <robdclark@gmail.com>
Reported-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

drivers/rpmsg/rpmsg_core.c

@@ -342,6 +342,11 @@ static ssize_t modalias_show(struct device *dev,
 			     struct device_attribute *attr, char *buf)
 {
 	struct rpmsg_device *rpdev = to_rpmsg_device(dev);
+	ssize_t len;
+
+	len = of_device_modalias(dev, buf, PAGE_SIZE);
+	if (len != -ENODEV)
+		return len;
 
 	return sprintf(buf, RPMSG_DEVICE_MODALIAS_FMT "\n", rpdev->id.name);
 }
@@ -384,6 +389,11 @@ static int rpmsg_dev_match(struct device *dev, struct device_driver *drv)
 static int rpmsg_uevent(struct device *dev, struct kobj_uevent_env *env)
 {
 	struct rpmsg_device *rpdev = to_rpmsg_device(dev);
+	int ret;
+
+	ret = of_device_uevent_modalias(dev, env);
+	if (ret != -ENODEV)
+		return ret;
 
 	return add_uevent_var(env, "MODALIAS=" RPMSG_DEVICE_MODALIAS_FMT,
 					rpdev->id.name);