Set DS4 BT HID-present flag and align tests

DualShock 4 Bluetooth input reports now set the HID-present header bit (0x80) while keeping existing BT framing and CRC behavior. This enables HIDAPI/SDL consumers to accept live input after hotplug on Linux. Updated report and Linux consumer tests to assert the new behavior, and refreshed platform-support docs to describe the BT report contract and unchanged transport boundaries.

Author: ReenigneArcher

docs/platform-support.md

@@ -141,8 +141,11 @@ provides it separately on the UHID event.
 The default DualShock 4 and DualSense profiles use Bluetooth framing, avoiding
 the parent-USB checks that can make virtual USB devices appear late in Steam.
 Explicit USB and Bluetooth factories remain available for consumers that
-require a particular transport. DualSense motion packing preserves the public
-meters-per-second-squared and degrees-per-second units while applying the same
+require a particular transport. DualShock 4 Bluetooth input reports set the
+HID-present header flag required by HIDAPI consumers and include the transport
+CRC, so a running consumer can accept live input after hotplug. DualSense motion
+packing preserves the public meters-per-second-squared and degrees-per-second
+units while applying the same
 raw sensor calibration used by Inputtino. Periodic PlayStation reports are
 repacked at 100 Hz so their sequence number and sensor timestamp continue to
 advance even when controller state is unchanged. Periodic and application
@@ -158,9 +161,8 @@ a controller before its kernel HID device has started.
 
 On Linux, DualShock 4 and DualSense emit Sony's native `Wireless Controller`
 product name for Steam HID discovery. The requested USB or Bluetooth bus,
-descriptor, and report framing remain unchanged; in particular, the default
-DualShock 4 profile stays on its USB report contract. This transport-only name
-is confined to the Linux backend; public profile names, Windows names, and VHF
+descriptor, and report framing remain unchanged. This transport-only name is
+confined to the Linux backend; public profile names, Windows names, and VHF
 behavior are unchanged.
 
 Switch Pro keeps its Nintendo identity on the Linux uinput path. This follows

src/core/report.cpp

@@ -33,6 +33,8 @@ namespace lvh::reports {
 
     constexpr auto dualshock4_bt_input_report_id = std::byte {0x11};
 
+    constexpr auto dualshock4_bt_input_hid_present = std::byte {0x80};
+
     constexpr auto dualshock4_bt_output_report_id = std::byte {0x11};
 
     constexpr auto dualshock4_output_hwctl_crc32 = std::byte {0x40};
@@ -646,6 +648,9 @@ namespace lvh::reports {
 
       ByteReport report(profile.input_report_size, zero_byte);
       report[0] = is_bluetooth ? dualshock4_bt_input_report_id : to_byte(profile.report_id);
+      if (is_bluetooth) {
+        report[1] = dualshock4_bt_input_hid_present;
+      }
 
       report[payload_offset + 0U] = to_byte(normalize_u8_axis(normalized.left_stick.x));
       report[payload_offset + 1U] = to_byte(normalize_u8_axis(-normalized.left_stick.y));

tests/fixtures/linux_backend_test_hooks.cpp

@@ -1868,7 +1868,11 @@ namespace lvh::detail::test {
 
     if (read_uhid_event_type(descriptors[1], UHID_INPUT2, event)) {
       const auto report_size = static_cast<std::size_t>(event.u.input2.size);
-      if (report_size == options.profile.input_report_size && event.u.input2.data[0] == 0x11) {
+      if (
+        report_size == options.profile.input_report_size &&
+        event.u.input2.data[0] == 0x11 &&
+        (event.u.input2.data[1] & 0x80U) != 0U
+      ) {
         const auto crc_offset = report_size - 4U;
         const auto expected_crc = crc32(std::span<const std::uint8_t> {event.u.input2.data, crc_offset}, playstation_crc_seed(0xA1));
         const auto actual_crc = read_u32_le(event.u.input2.data + crc_offset);

tests/unit/test_linux_consumers.cpp

@@ -886,7 +886,7 @@ TEST_F(LinuxConsumerTest, SdlSeesDualShock4UsbControllerBehavior) {
   });
 }
 
-TEST_F(LinuxConsumerTest, SdlSeesDualShock4BluetoothControllerDiscovery) {
+TEST_F(LinuxConsumerTest, SdlSeesDualShock4BluetoothControllerBehavior) {
   ASSERT_TRUE(HasReadableWritableDeviceNode("/dev/uhid"));
 
   run_sdl_playstation_controller_test({
@@ -895,7 +895,6 @@ TEST_F(LinuxConsumerTest, SdlSeesDualShock4BluetoothControllerDiscovery) {
     .stable_id = "02:00:00:00:00:04",
     .minimum_buttons = 10,
     .minimum_axes = 4,
-    .expect_live_input = false,
   });
 }
 

tests/unit/test_report.cpp

@@ -350,6 +350,7 @@ TEST(ReportTest, PacksDualShock4BluetoothReportWithCrc) {
 
   ASSERT_EQ(report.size(), profile.input_report_size);
   EXPECT_EQ(report[0], 0x11);
+  EXPECT_EQ(report[1], 0x80);
   EXPECT_EQ(report[3], 128);
   EXPECT_EQ(report[4], 128);
   EXPECT_EQ(report[9], 0x02);