test/py: dfu: error out if USB device already exists

The DFU test requests U-Boot configure its USB controller in device mode,
then waits for the host machine to enumerate the USB device and create a
device node for it. However, this wait can be fooled if the USB device
node already exists before the test starts, e.g. if some previous software
stack already configured the USB controller into device mode and never
de-configured it. This "previous software stack" could even be another
test/py test, if U-Boot's own USB teardown does not operate correctly. If
this happens, dfu-util may be run before U-Boot is ready to serve DFU
commands, which may cause false test failures.

Enhance the dfu test to fail if the device node exists before it is
expected to.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

diff --git a/test/py/tests/test_dfu.py b/test/py/tests/test_dfu.py
index cc4b8d8e04e615734a71fe7444c1fc5488615da3..6c1a363b02df0823d06eee1c0b3e5aa35183657c 100644 (file)
--- a/test/py/tests/test_dfu.py
+++ b/test/py/tests/test_dfu.py
@@ -100,6 +100,12 @@ def test_dfu(u_boot_console, env__usb_dev_port, env__dfu_config):
             Nothing.
         '''
 
+        fh = u_boot_utils.attempt_to_open_file(
+            env__usb_dev_port['host_usb_dev_node'])
+        if fh:
+            fh.close()
+            raise Exception('USB device present before dfu command invoked')
+
         u_boot_console.log.action(
             'Starting long-running U-Boot dfu shell command')