ipmi:ssif: Improve detecting during probing

If an IPMI SSIF device is probed and there is something there, but
probably not an actual BMC, the code would just issue a lot of errors
before it failed.  We kind of need these errors to help with certain
issues, and some of the failure reports are non-fatal.

However, a get device id command should alway work.  If that fails,
nothing else is going to work and it's a pretty good indication that
there's no valid BMC there.  So issue and check that command and bail
if it fails.
Reported-by: Ivan T. Ivanov <iivanov@suse.de>
Signed-off-by: Corey Minyard <corey@minyard.net>

drivers/char/ipmi/ipmi_ssif.c

@@ -1368,8 +1368,20 @@ static int ssif_detect(struct i2c_client *client, struct i2c_board_info *info)
 	rv = do_cmd(client, 2, msg, &len, resp);
 	if (rv)
 		rv = -ENODEV;
-	else
+	else {
+	    if (len < 3) {
+		rv = -ENODEV;
+	    } else {
+		struct ipmi_device_id id;
+
+		rv = ipmi_demangle_device_id(resp[0] >> 2, resp[1],
+					     resp + 2, len - 2, &id);
+		if (rv)
+		    rv = -ENODEV; /* Error means a BMC probably isn't there. */
+	    }
+	    if (!rv && info)
 		strscpy(info->type, DEVICE_NAME, I2C_NAME_SIZE);
+	}
 	kfree(resp);
 	return rv;
 }
@@ -1704,6 +1716,16 @@ static int ssif_probe(struct i2c_client *client)
 		ipmi_addr_src_to_str(ssif_info->addr_source),
 		client->addr, client->adapter->name, slave_addr);
 
+	/*
+	 * Send a get device id command and validate its response to
+	 * make sure a valid BMC is there.
+	 */
+	rv = ssif_detect(client, NULL);
+	if (rv) {
+		dev_err(&client->dev, "Not present\n");
+		goto out;
+	}
+
 	/* Now check for system interface capabilities */
 	msg[0] = IPMI_NETFN_APP_REQUEST << 2;
 	msg[1] = IPMI_GET_SYSTEM_INTERFACE_CAPABILITIES_CMD;