mfd: cros_ec: Use fixed size arrays to transfer data with the EC

The struct cros_ec_command will be used as an ioctl() argument for the
API to control the ChromeOS EC from user-space. So the data structure
has to be 64-bit safe to make it compatible between 32 and 64 avoiding
the need for a compat ioctl interface. Since pointers are self-aligned
to different byte boundaries, use fixed size arrays instead of pointers
for transferring ingoing and outgoing data with the Embedded Controller.

Also, re-arrange struct members by decreasing alignment requirements to
reduce the needing padding size.

Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Acked-by: Lee Jones <lee.jones@linaro.org>
Tested-by: Gwendal Grignou <gwendal@chromium.org>
Reviewed-by: Gwendal Grignou <gwendal@chromium.org>
Signed-off-by: Olof Johansson <olof@lixom.net>

drivers/i2c/busses/i2c-cros-ec-tunnel.c

@@ -182,72 +182,41 @@ static int ec_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg i2c_msgs[],
 	const u16 bus_num = bus->remote_bus;
 	int request_len;
 	int response_len;
-	u8 *request = NULL;
-	u8 *response = NULL;
 	int result;
-	struct cros_ec_command msg;
+	struct cros_ec_command msg = { };
 
 	request_len = ec_i2c_count_message(i2c_msgs, num);
 	if (request_len < 0) {
 		dev_warn(dev, "Error constructing message %d\n", request_len);
-		result = request_len;
-		goto exit;
+		return request_len;
 	}
+
 	response_len = ec_i2c_count_response(i2c_msgs, num);
 	if (response_len < 0) {
 		/* Unexpected; no errors should come when NULL response */
 		dev_warn(dev, "Error preparing response %d\n", response_len);
-		result = response_len;
-		goto exit;
+		return response_len;
 	}
 
-	if (request_len <= ARRAY_SIZE(bus->request_buf)) {
-		request = bus->request_buf;
-	} else {
-		request = kzalloc(request_len, GFP_KERNEL);
-		if (request == NULL) {
-			result = -ENOMEM;
-			goto exit;
-		}
-	}
-	if (response_len <= ARRAY_SIZE(bus->response_buf)) {
-		response = bus->response_buf;
-	} else {
-		response = kzalloc(response_len, GFP_KERNEL);
-		if (response == NULL) {
-			result = -ENOMEM;
-			goto exit;
-		}
-	}
-
-	result = ec_i2c_construct_message(request, i2c_msgs, num, bus_num);
+	result = ec_i2c_construct_message(msg.outdata, i2c_msgs, num, bus_num);
 	if (result)
-		goto exit;
+		return result;
 
 	msg.version = 0;
 	msg.command = EC_CMD_I2C_PASSTHRU;
-	msg.outdata = request;
 	msg.outsize = request_len;
-	msg.indata = response;
 	msg.insize = response_len;
 
 	result = cros_ec_cmd_xfer(bus->ec, &msg);
 	if (result < 0)
-		goto exit;
+		return result;
 
-	result = ec_i2c_parse_response(response, i2c_msgs, &num);
+	result = ec_i2c_parse_response(msg.indata, i2c_msgs, &num);
 	if (result < 0)
-		goto exit;
+		return result;
 
 	/* Indicate success by saying how many messages were sent */
-	result = num;
-exit:
-	if (request != bus->request_buf)
-		kfree(request);
-	if (response != bus->response_buf)
-		kfree(response);
-
-	return result;
+	return num;
 }
 
 static u32 ec_i2c_functionality(struct i2c_adapter *adap)