greybus: interface: retry enumeration of UniPro-only modules

Greybus modules will sometimes fail to send the mailbox poke and
erroneously be enumerated as UniPro-only modules. The root cause for
this on the module side is not fully understand, but it seems that this
may be due to "the bootrom bug:" a known problem with the bootrom where
linkup will occasionally fail because of a race condition.

Before the new hotplug code was implemented in the firmware, the SVC
would retry enumeration of modules that did not send the mailbox poke;
this patch ports that functionality to the AP.
Signed-off-by: Jeffrey Carlyle <jcarlyle@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/interface.c

@@ -447,7 +447,8 @@ static int gb_interface_activate_operation(struct gb_interface *intf)
 		return -ENODEV;
 	case GB_SVC_INTF_TYPE_UNIPRO:
 		dev_err(&intf->dev, "interface type UniPro not supported\n");
-		return -ENODEV;
+		/* FIXME: check if this is a Toshiba bridge before retrying? */
+		return -EAGAIN;
 	case GB_SVC_INTF_TYPE_GREYBUS:
 		break;
 	default:

drivers/staging/greybus/module.c

@@ -138,13 +138,32 @@ static void gb_module_register_interface(struct gb_interface *intf)
 	struct gb_module *module = intf->module;
 	u8 intf_id = intf->interface_id;
 	int ret;
+	int retries = 3;
 
 	mutex_lock(&intf->mutex);
 
+	while (retries--) {
 		ret = gb_interface_activate(intf);
+		if (ret != -EAGAIN)
+			break;
+	}
 	if (ret) {
 		dev_err(&module->dev, "failed to activate interface %u: %d\n",
 				intf_id, ret);
+
+		/*
+		 * -EAGAIN indicates that the Greybus operation
+		 * interface_activate determined the remote interface to be
+		 * UniPro-only.  At present, we assume a UniPro-only module
+		 * to be a Greybus module that failed to send its mailbox
+		 * poke.  There is some reason to believe that this is
+		 * because of a bug in the ES3 bootrom.  If we exhause our
+		 * retries trying to activate such an interface, convert
+		 * the error code back into a "no device" error.
+		 */
+		if (ret == -EAGAIN)
+			ret = -ENODEV;
+
 		gb_interface_add(intf);
 		goto err_unlock;
 	}