[bug report] platform/chrome: cros_ec_uart: Add transport layer

[Dan Carpenter <error27@gmail.com>]

Hello Bhanu Prakash Maiya,

The patch 04a8bdd135cc: "platform/chrome: cros_ec_uart: Add transport
layer" from Dec 27, 2022, leads to the following Smatch static
checker warning:

	drivers/platform/chrome/cros_ec_uart.c:152 cros_ec_uart_pkt_xfer()
	warn: 'ret' possible negative type promoted to high

drivers/platform/chrome/cros_ec_uart.c
    130 static int cros_ec_uart_pkt_xfer(struct cros_ec_device *ec_dev,
    131                                  struct cros_ec_command *ec_msg)
    132 {
    133         struct cros_ec_uart *ec_uart = ec_dev->priv;
    134         struct serdev_device *serdev = ec_uart->serdev;
    135         struct response_info *resp = &ec_uart->response;
    136         struct ec_host_response *host_response;
    137         unsigned int len;
                ^^^^^^^^^^^^^^^^

    138         int ret, i;
    139         u8 sum;
    140 
    141         len = cros_ec_prepare_tx(ec_dev, ec_msg);
    142         dev_dbg(ec_dev->dev, "Prepared len=%d\n", len);
    143 
    144         /* Setup for incoming response */
    145         resp->data = ec_dev->din;
    146         resp->max_size = ec_dev->din_size;
    147         resp->size = 0;
    148         resp->exp_len = 0;
    149         resp->status = 0;
    150 
    151         ret = serdev_device_write_buf(serdev, ec_dev->dout, len);
--> 152         if (ret < len) {

If serdev_device_write_buf() returns negative then type promotion means
this condition is false.  Write it like:

	if (ret < 0 || ret != len) {
		dev_err(ec_dev->dev, "Unable to write data\n");
		if (ret >= 0)
			ret = -EIO;
		goto exit;
	}

    153                 dev_err(ec_dev->dev, "Unable to write data\n");
    154                 ret = -EIO;
    155                 goto exit;
    156         }
    157 
    158         ret = wait_event_timeout(resp->wait_queue, resp->status,
    159                                  msecs_to_jiffies(EC_MSG_DEADLINE_MS));
    160         if (ret == 0) {
    161                 dev_warn(ec_dev->dev, "Timed out waiting for response.\n");
    162                 ret = -ETIMEDOUT;
    163                 goto exit;
    164         }
    165 
    166         if (resp->status < 0) {
    167                 ret = resp->status;
    168                 dev_warn(ec_dev->dev, "Error response received: %d\n", ret);
    169                 goto exit;
    170         }
    171 
    172         host_response = (struct ec_host_response *)ec_dev->din;
    173         ec_msg->result = host_response->result;
    174 
    175         if (host_response->data_len > ec_msg->insize) {
    176                 dev_err(ec_dev->dev, "Resp too long (%d bytes, expected %d)\n",
    177                         host_response->data_len, ec_msg->insize);
    178                 ret = -ENOSPC;


ret = -EINVAL;  (Unless you are discussing harddrives).

    179                 goto exit;
    180         }
    181 
    182         /* Validate checksum */
    183         sum = 0;
    184         for (i = 0; i < sizeof(*host_response) + host_response->data_len; i++)
    185                 sum += ec_dev->din[i];
    186 
    187         if (sum) {
    188                 dev_err(ec_dev->dev, "Bad packet checksum calculated %x\n", sum);
    189                 ret = -EBADMSG;
    190                 goto exit;
    191         }
    192 
    193         memcpy(ec_msg->data, ec_dev->din + sizeof(*host_response), host_response->data_len);
    194 
    195         ret = host_response->data_len;
    196 
    197 exit:
    198         /* Invalidate response buffer to guard against out of band rx data */
    199         resp->data = NULL;
    200 
    201         if (ec_msg->command == EC_CMD_REBOOT_EC)
    202                 msleep(EC_REBOOT_DELAY_MS);
    203 
    204         return ret;
    205 }

regards,
dan carpenter