selftests/hid: tablets: be stricter for some transitions

To accommodate for legacy devices, we rely on the last state of a
transition to be valid:
for example when we test PEN_IS_OUT_OF_RANGE to PEN_IS_IN_CONTACT,
any "normal" device that reports an InRange bit would insert a
PEN_IS_IN_RANGE state between the 2.

This is of course valid, but this solution prevents to detect false
releases emitted by some firmware:
when pressing an "eraser mode" button, they might send an extra
PEN_IS_OUT_OF_RANGE that we may want to filter.

So define 2 sets of transitions: one that is the ideal behavior, and
one that is OK, it won't break user space, but we have serious doubts
if we are doing the right thing. And depending on the test, either
ask only for valid transitions, or tolerate weird ones.

Reviewed-by: Peter Hutterer <[e-mail]>
Acked-by: Jiri Kosina <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Benjamin Tissoires <[e-mail]>

tools/testing/selftests/hid/tests/test_tablet.py

···
 import libevdev
 import logging
 import pytest
-from typing import Dict, Optional, Tuple
+from typing import Dict, List, Optional, Tuple
 
 logger = logging.getLogger("hidtools.test.tablet")
 
···
 
         return cls((touch, tool, button))
 
-    def apply(self, events) -> "PenState":
+    def apply(self, events: List[libevdev.InputEvent], strict: bool) -> "PenState":
         if libevdev.EV_SYN.SYN_REPORT in events:
             raise ValueError("EV_SYN is in the event sequence")
         touch = self.touch
···
             button = None
 
         new_state = PenState((touch, tool, button))
-        assert (
-            new_state in self.valid_transitions()
-        ), f"moving from {self} to {new_state} is forbidden"
+        if strict:
+            assert (
+                new_state in self.valid_transitions()
+            ), f"moving from {self} to {new_state} is forbidden"
+        else:
+            assert (
+                new_state in self.historically_tolerated_transitions()
+            ), f"moving from {self} to {new_state} is forbidden"
 
         return new_state
 
     def valid_transitions(self) -> Tuple["PenState", ...]:
+        """Following the state machine in the URL above.
+
+        Note that those transitions are from the evdev point of view, not HID"""
+        if self == PenState.PEN_IS_OUT_OF_RANGE:
+            return (
+                PenState.PEN_IS_OUT_OF_RANGE,
+                PenState.PEN_IS_IN_RANGE,
+                PenState.PEN_IS_IN_RANGE_WITH_BUTTON,
+                PenState.PEN_IS_IN_RANGE_WITH_SECOND_BUTTON,
+                PenState.PEN_IS_IN_RANGE_WITH_ERASING_INTENT,
+                PenState.PEN_IS_IN_CONTACT,
+                PenState.PEN_IS_IN_CONTACT_WITH_BUTTON,
+                PenState.PEN_IS_IN_CONTACT_WITH_SECOND_BUTTON,
+                PenState.PEN_IS_ERASING,
+            )
+
+        if self == PenState.PEN_IS_IN_RANGE:
+            return (
+                PenState.PEN_IS_IN_RANGE,
+                PenState.PEN_IS_IN_RANGE_WITH_BUTTON,
+                PenState.PEN_IS_IN_RANGE_WITH_SECOND_BUTTON,
+                PenState.PEN_IS_OUT_OF_RANGE,
+                PenState.PEN_IS_IN_CONTACT,
+            )
+
+        if self == PenState.PEN_IS_IN_CONTACT:
+            return (
+                PenState.PEN_IS_IN_CONTACT,
+                PenState.PEN_IS_IN_CONTACT_WITH_BUTTON,
+                PenState.PEN_IS_IN_CONTACT_WITH_SECOND_BUTTON,
+                PenState.PEN_IS_IN_RANGE,
+            )
+
+        if self == PenState.PEN_IS_IN_RANGE_WITH_ERASING_INTENT:
+            return (
+                PenState.PEN_IS_IN_RANGE_WITH_ERASING_INTENT,
+                PenState.PEN_IS_OUT_OF_RANGE,
+                PenState.PEN_IS_ERASING,
+            )
+
+        if self == PenState.PEN_IS_ERASING:
+            return (
+                PenState.PEN_IS_ERASING,
+                PenState.PEN_IS_IN_RANGE_WITH_ERASING_INTENT,
+            )
+
+        if self == PenState.PEN_IS_IN_RANGE_WITH_BUTTON:
+            return (
+                PenState.PEN_IS_IN_RANGE_WITH_BUTTON,
+                PenState.PEN_IS_IN_RANGE,
+                PenState.PEN_IS_OUT_OF_RANGE,
+                PenState.PEN_IS_IN_CONTACT_WITH_BUTTON,
+            )
+
+        if self == PenState.PEN_IS_IN_CONTACT_WITH_BUTTON:
+            return (
+                PenState.PEN_IS_IN_CONTACT_WITH_BUTTON,
+                PenState.PEN_IS_IN_CONTACT,
+                PenState.PEN_IS_IN_RANGE_WITH_BUTTON,
+            )
+
+        if self == PenState.PEN_IS_IN_RANGE_WITH_SECOND_BUTTON:
+            return (
+                PenState.PEN_IS_IN_RANGE_WITH_SECOND_BUTTON,
+                PenState.PEN_IS_IN_RANGE,
+                PenState.PEN_IS_OUT_OF_RANGE,
+                PenState.PEN_IS_IN_CONTACT_WITH_SECOND_BUTTON,
+            )
+
+        if self == PenState.PEN_IS_IN_CONTACT_WITH_SECOND_BUTTON:
+            return (
+                PenState.PEN_IS_IN_CONTACT_WITH_SECOND_BUTTON,
+                PenState.PEN_IS_IN_CONTACT,
+                PenState.PEN_IS_IN_RANGE_WITH_SECOND_BUTTON,
+            )
+
+        return tuple()
+
+    def historically_tolerated_transitions(self) -> Tuple["PenState", ...]:
         """Following the state machine in the URL above, with a couple of addition
         for skipping the in-range state, due to historical reasons.
 
···
             self.debug_reports(r, uhdev, events)
             return events
 
-        def validate_transitions(self, from_state, pen, evdev, events):
+        def validate_transitions(
+            self, from_state, pen, evdev, events, allow_intermediate_states
+        ):
             # check that the final state is correct
             pen.assert_expected_input_events(evdev)
+
+            state = from_state
 
             # check that the transitions are valid
             sync_events = []
···
                 events = events[idx + 1 :]
 
                 # now check for a valid transition
-                from_state = from_state.apply(sync_events)
+                state = state.apply(sync_events, not allow_intermediate_states)
 
             if events:
-                from_state = from_state.apply(sync_events)
+                state = state.apply(sync_events, not allow_intermediate_states)
 
-        def _test_states(self, state_list, scribble):
+        def _test_states(self, state_list, scribble, allow_intermediate_states):
             """Internal method to test against a list of
             transition between states.
             state_list is a list of PenState objects
···
             p = Pen(50, 60)
             uhdev.move_to(p, PenState.PEN_IS_OUT_OF_RANGE)
             events = self.post(uhdev, p)
-            self.validate_transitions(cur_state, p, evdev, events)
+            self.validate_transitions(
+                cur_state, p, evdev, events, allow_intermediate_states
+            )
 
             cur_state = p.current_state
 
···
                     p.x += 1
                     p.y -= 1
                     events = self.post(uhdev, p)
-                    self.validate_transitions(cur_state, p, evdev, events)
+                    self.validate_transitions(
+                        cur_state, p, evdev, events, allow_intermediate_states
+                    )
                     assert len(events) >= 3  # X, Y, SYN
                 uhdev.move_to(p, state)
                 if scribble and state != PenState.PEN_IS_OUT_OF_RANGE:
                     p.x += 1
                     p.y -= 1
                 events = self.post(uhdev, p)
-                self.validate_transitions(cur_state, p, evdev, events)
+                self.validate_transitions(
+                    cur_state, p, evdev, events, allow_intermediate_states
+                )
                 cur_state = p.current_state
 
         @pytest.mark.parametrize("scribble", [True, False], ids=["scribble", "static"])
···
             we don't have Invert nor Erase bits, so just move in/out-of-range or proximity.
             https://docs.microsoft.com/en-us/windows-hardware/design/component-guidelines/windows-pen-states
             """
-            self._test_states(state_list, scribble)
+            self._test_states(state_list, scribble, allow_intermediate_states=False)
 
         @pytest.mark.parametrize("scribble", [True, False], ids=["scribble", "static"])
         @pytest.mark.parametrize(
···
             """This is not adhering to the Windows Pen Implementation state machine
             but we should expect the kernel to behave properly, mostly for historical
             reasons."""
-            self._test_states(state_list, scribble)
+            self._test_states(state_list, scribble, allow_intermediate_states=True)
 
         @pytest.mark.skip_if_uhdev(
             lambda uhdev: "Barrel Switch" not in uhdev.fields,
···
         )
         def test_valid_primary_button_pen_states(self, state_list, scribble):
             """Rework the transition state machine by adding the primary button."""
-            self._test_states(state_list, scribble)
+            self._test_states(state_list, scribble, allow_intermediate_states=False)
 
         @pytest.mark.skip_if_uhdev(
             lambda uhdev: "Secondary Barrel Switch" not in uhdev.fields,
···
         )
         def test_valid_secondary_button_pen_states(self, state_list, scribble):
             """Rework the transition state machine by adding the secondary button."""
-            self._test_states(state_list, scribble)
+            self._test_states(state_list, scribble, allow_intermediate_states=False)
 
         @pytest.mark.skip_if_uhdev(
             lambda uhdev: "Invert" not in uhdev.fields,
···
             to erase.
             https://docs.microsoft.com/en-us/windows-hardware/design/component-guidelines/windows-pen-states
             """
-            self._test_states(state_list, scribble)
+            self._test_states(state_list, scribble, allow_intermediate_states=False)
 
         @pytest.mark.skip_if_uhdev(
             lambda uhdev: "Invert" not in uhdev.fields,
···
             to erase.
             https://docs.microsoft.com/en-us/windows-hardware/design/component-guidelines/windows-pen-states
             """
-            self._test_states(state_list, scribble)
+            self._test_states(state_list, scribble, allow_intermediate_states=True)
 
         @pytest.mark.skip_if_uhdev(
             lambda uhdev: "Invert" not in uhdev.fields,
···
             For example, a pen that has the eraser button might wobble between
             touching and erasing if the tablet doesn't enforce the Windows
             state machine."""
-            self._test_states(state_list, scribble)
+            self._test_states(state_list, scribble, allow_intermediate_states=True)
 
 
 class GXTP_pen(PenDigitizer):