greybus: svc: reconfig APBridgeA-Switch link to handle required load

SW-4894, SW-4389, and share a common root cause, namely that
the power-on reset configuration of the APBridgeA-Switch link of PWM
Gear 1, 1 Lane, Slow Auto, is insufficient to handle some required
traffic loads, such as 3 audio streams plus boot-over-UniPro or 4 audio
streams.

The correct long-term solution is to implement a UniPro Power Mode
Manager as in that considers the demands placed on the network,
and adjusts power modes accordingly.

The present commit implements a short-term, brute-force hack to allow
continued system testing:
- Upon receiving an SVC HELLO request, schedule deferred work to
  reconfigure the APB1-Switch link to PWM G2, 1 lane, Slow Auto
- When the Camera driver transitions a White Camera module from active to
  inactive, return the APB1-Switch link to PWM G2, 1 lane, Slow Auto

The Camera driver already steps up the APBridgeA-Camera link speed while a
camera module is active, which affords sufficient margin for simultaneous
audio and hotplug activity, and the Camera driver already steps down the
link speed thereafter: the change made by the present patch is simply to
tweak the stepped-down power mode to match the new baseline configuration.

Signed-off-by: Mitchell Tasman <tasman@leaflabs.com>
Tested-by: Mark Greer <mgreer@animalcreek.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/camera.c

@@ -131,9 +131,9 @@ static int gb_camera_set_intf_power_mode(struct gb_camera *gcam, u8 intf_id,
 		ret = gb_svc_intf_set_power_mode(svc, intf_id,
 						 GB_SVC_UNIPRO_HS_SERIES_A,
 						 GB_SVC_UNIPRO_SLOW_AUTO_MODE,
-						 1, 2,
+						 2, 1,
 						 GB_SVC_UNIPRO_SLOW_AUTO_MODE,
-						 1, 2,
+						 2, 1,
 						 0, 0);
 
 	return ret;

drivers/staging/greybus/svc.c

@@ -23,6 +23,8 @@ struct gb_svc_deferred_request {
 };
 
 
+static int gb_svc_queue_deferred_request(struct gb_operation *operation);
+
 static ssize_t endo_id_show(struct device *dev,
 			struct device_attribute *attr, char *buf)
 {
@@ -695,7 +697,7 @@ static int gb_svc_hello(struct gb_operation *op)
 
 	gb_svc_debugfs_init(svc);
 
-	return 0;
+	return gb_svc_queue_deferred_request(op);
 }
 
 static struct gb_interface *gb_svc_interface_lookup(struct gb_svc *svc,
@@ -754,6 +756,35 @@ static void gb_svc_intf_reenable(struct gb_svc *svc, struct gb_interface *intf)
 	mutex_unlock(&intf->mutex);
 }
 
+static void gb_svc_process_hello_deferred(struct gb_operation *operation)
+{
+	struct gb_connection *connection = operation->connection;
+	struct gb_svc *svc = gb_connection_get_data(connection);
+	int ret;
+
+	/*
+	 * XXX This is a hack/work-around to reconfigure the APBridgeA-Switch
+	 * link to PWM G2, 1 Lane, Slow Auto, so that it has sufficient
+	 * bandwidth for 3 audio streams plus boot-over-UniPro of a hot-plugged
+	 * module.
+	 *
+	 * The code should be removed once SW-2217, Heuristic for UniPro
+	 * Power Mode Changes is resolved.
+	 */
+	ret = gb_svc_intf_set_power_mode(svc, svc->ap_intf_id,
+					GB_SVC_UNIPRO_HS_SERIES_A,
+					GB_SVC_UNIPRO_SLOW_AUTO_MODE,
+					2, 1,
+					GB_SVC_UNIPRO_SLOW_AUTO_MODE,
+					2, 1,
+					0, 0);
+
+	if (ret)
+		dev_warn(&svc->dev,
+			"power mode change failed on AP to switch link: %d\n",
+			ret);
+}
+
 static void gb_svc_process_intf_hotplug(struct gb_operation *operation)
 {
 	struct gb_svc_intf_hotplug_request *request;
@@ -963,6 +994,9 @@ static void gb_svc_process_deferred_request(struct work_struct *work)
 	type = operation->request->header->type;
 
 	switch (type) {
+	case GB_SVC_TYPE_SVC_HELLO:
+		gb_svc_process_hello_deferred(operation);
+		break;
 	case GB_SVC_TYPE_INTF_HOTPLUG:
 		gb_svc_process_intf_hotplug(operation);
 		break;