linux: If the kernel specifically tells us the device type, trust it

If a device is positively identified as an accelerometer, pointing stick
or clickpad, then we don't need to second-guess it.

In practice this does not change the result for any device in our
test data, so add some artificial records that exercise this.

Signed-off-by: Simon McVittie <smcv@collabora.com>

src/core/linux/SDL_evdev_capabilities.c

@@ -58,6 +58,22 @@ SDL_EVDEV_GuessDeviceClass(const unsigned long bitmask_props[NBITS(INPUT_PROP_MA
     int devclass = 0;
     unsigned long keyboard_mask;
 
+    /* If the kernel specifically says it's an accelerometer, believe it */
+    if (test_bit(INPUT_PROP_ACCELEROMETER, bitmask_props)) {
+        return SDL_UDEV_DEVICE_ACCELEROMETER;
+    }
+
+    /* We treat pointing sticks as indistinguishable from mice */
+    if (test_bit(INPUT_PROP_POINTING_STICK, bitmask_props)) {
+        return SDL_UDEV_DEVICE_MOUSE;
+    }
+
+    /* We treat buttonpads as equivalent to touchpads */
+    if (test_bit(INPUT_PROP_TOPBUTTONPAD, bitmask_props) ||
+        test_bit(INPUT_PROP_BUTTONPAD, bitmask_props)) {
+        return SDL_UDEV_DEVICE_TOUCHPAD;
+    }
+
     /* X, Y, Z axes but no buttons probably means an accelerometer */
     if (test_bit(EV_ABS, bitmask_ev) &&
         test_bit(ABS_X, bitmask_abs) &&
@@ -67,7 +83,8 @@ SDL_EVDEV_GuessDeviceClass(const unsigned long bitmask_props[NBITS(INPUT_PROP_MA
         return SDL_UDEV_DEVICE_ACCELEROMETER;
     }
 
-    /* RX, RY, RZ axes but no buttons also probably means an accelerometer */
+    /* RX, RY, RZ axes but no buttons probably means a gyro or
+     * accelerometer (we don't distinguish) */
     if (test_bit(EV_ABS, bitmask_ev) &&
         test_bit(ABS_RX, bitmask_abs) &&
         test_bit(ABS_RY, bitmask_abs) &&

test/testevdev.c

@@ -1758,6 +1758,36 @@ static const GuessTest guess_tests[] =
       .hid_report_descriptor_length = sizeof (fanatec_handbrake_hid_report_descriptor),
       .hid_report_descriptor = &fanatec_handbrake_hid_report_descriptor[0],
     },
+    { /* Artificial test data, not a real device */
+      .name = "Fake accelerometer with fewer than usual axes reported",
+      .expected = SDL_UDEV_DEVICE_ACCELEROMETER,
+      /* SYN, ABS */
+      .ev = { 0x09 },
+      /* X only */
+      .abs = { 0x01 },
+      /* ACCELEROMETER */
+      .props = { 0x40 },
+    },
+    { /* Artificial test data, not a real device */
+      .name = "Fake pointing stick with no buttons",
+      .expected = SDL_UDEV_DEVICE_MOUSE,
+      /* SYN, REL */
+      .ev = { 0x05 },
+      /* X,Y */
+      .rel = { 0x03 },
+      /* POINTER, POINTING_STICK */
+      .props = { 0x21 },
+    },
+    { /* Artificial test data, not a real device */
+      .name = "Fake buttonpad",
+      .expected = SDL_UDEV_DEVICE_TOUCHPAD,
+      /* SYN, ABS */
+      .ev = { 0x09 },
+      /* X,Y */
+      .abs = { 0x03 },
+      /* POINTER, BUTTONPAD */
+      .props = { 0x05 },
+    },
     {
       .name = "No information",
       .expected = SDL_UDEV_DEVICE_UNKNOWN,