greybus: interface: do not read DME during reactivation

It will soon be possible to reactivate an interface that has been
powered down after already having been activated. In that case there's
no need to re-read the DME attributes as part of activation as the
values are already cached.
Reviewed-by: Sandeep Patil <sspatil@google.com>
Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Reviewed-by: Alex Elder <elder@linaro.org>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Patrick Titiano <ptitiano@baylibre.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/interface.c

@@ -95,6 +95,10 @@ static int gb_interface_read_dme(struct gb_interface *intf)
 {
 	int ret;
 
+	/* DME attributes have already been read */
+	if (intf->dme_read)
+		return 0;
+
 	ret = gb_interface_dme_attr_get(intf, DME_DDBL1_MANUFACTURERID,
 					&intf->ddbl1_manufacturer_id);
 	if (ret)
@@ -111,7 +115,13 @@ static int gb_interface_read_dme(struct gb_interface *intf)
 		intf->quirks |= GB_INTERFACE_QUIRK_NO_INIT_STATUS;
 	}
 
-	return gb_interface_read_ara_dme(intf);
+	ret = gb_interface_read_ara_dme(intf);
+	if (ret)
+		return ret;
+
+	intf->dme_read = true;
+
+	return 0;
 }
 
 static int gb_interface_route_create(struct gb_interface *intf)

drivers/staging/greybus/interface.h

@@ -56,6 +56,7 @@ struct gb_interface {
 	bool active;
 	bool enabled;
 	bool mode_switch;
+	bool dme_read;
 
 	struct work_struct mode_switch_work;
 	struct completion mode_switch_completion;