Tests: USBHID: Make report test optional on Linux

This test case uses `hidapi` -- a cross-platform Python module.
To keep the initial Mbed setup as simple as possible, the `hidapi`
module is skipped on Linux hosts because of its external dependancies
for this platform.

The module can be easily installed following instructions from the
README file.
The test case is skipped if the host machine lacks `hidapi` module.

TESTS/host_tests/usb_device_hid.py

@@ -20,7 +20,6 @@ import time
 import threading
 import uuid
 import mbed_host_tests
-import hid
 import usb.core
 from usb.util import (
     CTRL_IN,
@@ -32,6 +31,12 @@ from usb.util import (
     DESC_TYPE_CONFIG,
     build_request_type)
 
+try:
+    import hid
+except ImportError:
+    CYTHON_HIDAPI_PRESENT = False
+else:
+    CYTHON_HIDAPI_PRESENT = True
 
 # USB device -- device classes
 USB_CLASS_HID = 0x03
@@ -81,6 +86,7 @@ MSG_KEY_TEST_RAW_IO = 'test_raw_io'
 MSG_KEY_TEST_CASE_FAILED = 'fail'
 MSG_KEY_TEST_CASE_PASSED = 'pass'
 MSG_VALUE_DUMMY = '0'
+MSG_VALUE_NOT_SUPPORTED = 'not_supported'
 
 # Constants for the tests.
 KEYBOARD_IDLE_RATE_TO_SET = 0x00  # Duration = 0 (indefinite)
@@ -95,6 +101,8 @@ def build_get_desc_value(desc_type, desc_index):
 
 def usb_hid_path(serial_number):
     """Get a USB HID device system path based on the serial number."""
+    if not CYTHON_HIDAPI_PRESENT:
+        return None
     for device_info in hid.enumerate():  # pylint: disable=no-member
         if device_info.get('serial_number') == serial_number:  # pylint: disable=not-callable
             return device_info['path']
@@ -544,6 +552,9 @@ class USBHIDTest(mbed_host_tests.BaseHostTest):
 
     def cb_test_raw_io(self, key, value, timestamp):
         """Receive HID reports and send them back to the device."""
+        if not CYTHON_HIDAPI_PRESENT:
+            self.send_kv(MSG_KEY_HOST_READY, MSG_VALUE_NOT_SUPPORTED)
+            return
         try:
             # The size of input and output reports used in test.
             report_size = int(value)

TESTS/usb_device/hid/README.md

@@ -0,0 +1,23 @@
+# Testing the USB HID device with a Linux host
+
+Before running `tests-usb_device-hid` test suite on a Linux machine, please
+make sure to install the `hidapi` Python module first, otherwise some test
+cases will be skipped. Due to external dependencies for Linux, this module
+is not installed during the initial setup, to keep the process as simple
+as possible.
+
+For Debian-based Linux distros, the dependencies can be installed as follows
+(based on module's [README][1]):
+
+```bash
+apt-get install python-dev libusb-1.0-0-dev libudev-dev
+pip install --upgrade setuptools
+```
+To install the `hidapi` module itself, please use the attached
+`TESTS/usb_device/hid/requirements.txt` file:
+```bash
+pip install -r requirements.txt
+```
+
+[1]: https://github.com/trezor/cython-hidapi/blob/master/README.rst#install
+

TESTS/usb_device/hid/main.cpp

@@ -49,6 +49,7 @@
 #define MSG_KEY_TEST_CASE_FAILED "fail"
 #define MSG_KEY_TEST_CASE_PASSED "pass"
 #define MSG_VALUE_DUMMY "0"
+#define MSG_VALUE_NOT_SUPPORTED "not_supported"
 
 #define RAW_IO_REPS 16
 
@@ -310,6 +311,10 @@ void test_generic_raw_io()
     char value[MSG_VALUE_LEN + 1] = { };
     greentea_parse_kv(key, value, MSG_KEY_LEN, MSG_VALUE_LEN);
     TEST_ASSERT_EQUAL_STRING(MSG_KEY_HOST_READY, key);
+    if (strcmp(value, MSG_VALUE_NOT_SUPPORTED) == 0) {
+        TEST_IGNORE_MESSAGE("Test case not supported by host plarform.");
+        return;
+    }
 
     // Report ID omitted here. There are no Report ID tags in the Report descriptor.
     HID_REPORT input_report = {};

TESTS/usb_device/hid/requirements.txt

@@ -0,0 +1 @@
+hidapi>=0.7.99,<0.8.0

requirements.txt

@@ -21,5 +21,5 @@ manifest-tool==1.4.8
 icetea>=1.2.1,<1.3
 pycryptodome>=3.7.2,<=3.7.3
 pyusb>=1.0.0,<2.0.0
-hidapi>=0.7.99,<0.8.0
+hidapi>=0.7.99,<0.8.0;platform_system!="Linux"
 cmsis-pack-manager>=0.2.3,<0.3.0