greybus: interface: implement generic mode-switch functionality

Add a generic interface for bundle drivers to use to request that a
mode switch is carried out on its behalf.

Mode switching involves tearing down all connections to an interface,
sending a unidirectional mode-switch request, and waiting for a mailbox
event that triggers deferred control connection reset and re-enumeration
of the interface. In case of a timeout waiting for the interface mailbox
event, or on other errors, the interface is powered off.

All of this needs to be done by core from work-queue context in order
not to block incoming SVC requests and bundle-device tear down. Care
must also be taken to serialise against concurrent module removal events
and eject requests.

Special handling of legacy mode-switching is also added in order to
continue to support the ES3 bootrom.

Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

1 files changed, 32 insertions, 4 deletions

diff --git a/drivers/staging/greybus/connection.c b/drivers/staging/greybus/connection.c
index c1cdfcd830a4..3be767b9a0de 100644
--- a/drivers/staging/greybus/connection.c
+++ b/drivers/staging/greybus/connection.c
@@ -487,10 +487,23 @@ gb_connection_control_disconnected(struct gb_connection *connection)
 	if (gb_connection_is_static(connection))
 		return;
 
-	if (gb_connection_is_control(connection))
+	control = connection->intf->control;
+
+	if (gb_connection_is_control(connection)) {
+		if (connection->mode_switch) {
+			ret = gb_control_mode_switch_operation(control);
+			if (ret) {
+				/*
+				 * Allow mode switch to time out waiting for
+				 * mailbox event.
+				 */
+				return;
+			}
+		}
+
 		return;
+	}
 
-	control = connection->intf->control;
 
 	ret = gb_control_disconnected_operation(control, cport_id);
 	if (ret) {
@@ -743,6 +756,18 @@ out_unlock:
 }
 EXPORT_SYMBOL_GPL(gb_connection_disable_rx);
 
+void gb_connection_mode_switch_prepare(struct gb_connection *connection)
+{
+	connection->mode_switch = true;
+}
+
+void gb_connection_mode_switch_complete(struct gb_connection *connection)
+{
+	gb_connection_svc_connection_destroy(connection);
+	gb_connection_hd_cport_disable(connection);
+	connection->mode_switch = false;
+}
+
 void gb_connection_disable(struct gb_connection *connection)
 {
 	mutex_lock(&connection->mutex);
@@ -768,8 +793,11 @@ void gb_connection_disable(struct gb_connection *connection)
 
 	connection->state = GB_CONNECTION_STATE_DISABLED;
 
-	gb_connection_svc_connection_destroy(connection);
-	gb_connection_hd_cport_disable(connection);
+	/* control-connection tear down is deferred when mode switching */
+	if (!connection->mode_switch) {
+		gb_connection_svc_connection_destroy(connection);
+		gb_connection_hd_cport_disable(connection);
+	}
 
 out_unlock:
 	mutex_unlock(&connection->mutex);