i3c: Add a modalias sysfs attribute

Create a modalias sysfs attribute for i3c devices.
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Vitor Soares <vitor.soares@synopsys.com>
Link: https://lore.kernel.org/linux-i3c/a90f64f830128cd12762153de7828b775574c156.1582796652.git.vitor.soares@synopsys.com

drivers/i3c/master.c

@@ -241,12 +241,34 @@ static ssize_t hdrcap_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(hdrcap);
 
+static ssize_t modalias_show(struct device *dev,
+			     struct device_attribute *da, char *buf)
+{
+	struct i3c_device *i3c = dev_to_i3cdev(dev);
+	struct i3c_device_info devinfo;
+	u16 manuf, part, ext;
+
+	i3c_device_get_info(i3c, &devinfo);
+	manuf = I3C_PID_MANUF_ID(devinfo.pid);
+	part = I3C_PID_PART_ID(devinfo.pid);
+	ext = I3C_PID_EXTRA_INFO(devinfo.pid);
+
+	if (I3C_PID_RND_LOWER_32BITS(devinfo.pid))
+		return sprintf(buf, "i3c:dcr%02Xmanuf%04X", devinfo.dcr,
+			       manuf);
+
+	return sprintf(buf, "i3c:dcr%02Xmanuf%04Xpart%04Xext%04X",
+		       devinfo.dcr, manuf, part, ext);
+}
+static DEVICE_ATTR_RO(modalias);
+
 static struct attribute *i3c_device_attrs[] = {
 	&dev_attr_bcr.attr,
 	&dev_attr_dcr.attr,
 	&dev_attr_pid.attr,
 	&dev_attr_dynamic_address.attr,
 	&dev_attr_hdrcap.attr,
+	&dev_attr_modalias.attr,
 	NULL,
 };
 ATTRIBUTE_GROUPS(i3c_device);