powerpc/powernv: handle OPAL_SUCCESS return in opal_sensor_read

Currently, when a sensor value is read, the kernel calls OPAL, which in
turn builds a message for the FSP, and waits for a message back.

The new device tree for OPAL sensors [1] adds new sensors that can be
read synchronously (core temperatures for instance) and that don't need
to wait for a response.

This patch modifies the opal call to accept an OPAL_SUCCESS return value
and cover the case above.

[1] https://lists.ozlabs.org/pipermail/skiboot/2015-March/000639.html

Signed-off-by: Cédric Le Goater <clg@fr.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/powernv/opal-sensor.c

@@ -46,20 +46,28 @@ int opal_get_sensor_data(u32 sensor_hndl, u32 *sensor_data)
 
 	mutex_lock(&opal_sensor_mutex);
 	ret = opal_sensor_read(sensor_hndl, token, &data);
-	if (ret != OPAL_ASYNC_COMPLETION) {
-		ret = opal_error_code(ret);
-		goto out_token;
-	}
+	switch (ret) {
+	case OPAL_ASYNC_COMPLETION:
+		ret = opal_async_wait_response(token, &msg);
+		if (ret) {
+			pr_err("%s: Failed to wait for the async response, %d\n",
+			       __func__, ret);
+			goto out_token;
+		}
 
-	ret = opal_async_wait_response(token, &msg);
-	if (ret) {
-		pr_err("%s: Failed to wait for the async response, %d\n",
-				__func__, ret);
-		goto out_token;
-	}
+		ret = opal_error_code(be64_to_cpu(msg.params[1]));
+		*sensor_data = be32_to_cpu(data);
+		break;
 
-	*sensor_data = be32_to_cpu(data);
-	ret = opal_error_code(be64_to_cpu(msg.params[1]));
+	case OPAL_SUCCESS:
+		ret = 0;
+		*sensor_data = be32_to_cpu(data);
+		break;
+
+	default:
+		ret = opal_error_code(ret);
+		break;
+	}
 
 out_token:
 	mutex_unlock(&opal_sensor_mutex);