greybus: interface: Expose DDBL1 manufacturing and production id in sysfs

These ids are already fetched from the SVC, but were never exposed to
sysfs. Userspace may be interested in using these values and hence these
must be exposed to it.
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/Documentation/sysfs-bus-greybus

@@ -14,6 +14,22 @@ Description:
 		An Interface I on the bus N, where I is the 1-byte interface
 		ID.
 
+What:		/sys/bus/greybus/device/N-I/ddbl1_manufacturer_id
+Date:		October 2015
+KernelVersion:	4.XX
+Contact:	Greg Kroah-Hartman <greg@kroah.com>
+Description:
+		Unipro Device Descriptor Block Level 1 manufacturer ID for the
+		greybus Interface.
+
+What:		/sys/bus/greybus/device/N-I/ddbl1_product_id
+Date:		October 2015
+KernelVersion:	4.XX
+Contact:	Greg Kroah-Hartman <greg@kroah.com>
+Description:
+		Unipro Device Descriptor Block Level 1 product ID for the
+		greybus Interface.
+
 What:		/sys/bus/greybus/device/N-I/interface_id
 Date:		October 2015
 KernelVersion:	4.XX

drivers/staging/greybus/interface.c

@@ -20,6 +20,8 @@ static ssize_t field##_show(struct device *dev,				\
 }									\
 static DEVICE_ATTR_RO(field)
 
+gb_interface_attr(ddbl1_manufacturer_id, "0x%08x");
+gb_interface_attr(ddbl1_product_id, "0x%08x");
 gb_interface_attr(interface_id, "%u");
 gb_interface_attr(vendor_id, "0x%08x");
 gb_interface_attr(product_id, "0x%08x");
@@ -27,6 +29,8 @@ gb_interface_attr(vendor_string, "%s");
 gb_interface_attr(product_string, "%s");
 
 static struct attribute *interface_attrs[] = {
+	&dev_attr_ddbl1_manufacturer_id.attr,
+	&dev_attr_ddbl1_product_id.attr,
 	&dev_attr_interface_id.attr,
 	&dev_attr_vendor_id.attr,
 	&dev_attr_product_id.attr,