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The MediaTek MT7927 (Filogic 380) combo WiFi 7 + BT 5.4 module uses hardware variant 0x6639 for its Bluetooth subsystem. Without this patch, the chip fails with "Unsupported hardware variant (00006639)" or hangs during firmware download. Three changes are needed to support MT6639: 1. CHIPID workaround: On some boards the BT USB MMIO register reads 0x0000 for dev_id, causing the driver to skip the 0x6639 init path. Force dev_id to 0x6639 only when the USB VID/PID matches a known MT6639 device, avoiding misdetection if a future chip also reads zero. This follows the WiFi-side pattern that uses PCI device IDs to scope the same workaround. 2. Firmware naming: MT6639 uses firmware version prefix "2_1" instead of "1_1" used by MT7925 and other variants. The firmware path is mediatek/mt7927/BT_RAM_CODE_MT6639_2_1_hdr.bin, using the mt7927 directory to match the WiFi firmware convention. The filename will likely change to use MT7927 once MediaTek submits a dedicated Linux firmware binary. 3. Section filtering: The MT6639 firmware binary contains 9 sections, but only sections with (dlmodecrctype & 0xff) == 0x01 are Bluetooth-related. Sending the remaining WiFi/other sections causes an irreversible BT subsystem hang requiring a full power cycle. This matches the Windows driver behavior observed via USB captures. Also add 0x6639 to the reset register (CONNV3) and firmware setup switch cases alongside the existing 0x7925 handling. Link: https://bugzilla.kernel.org/show_bug.cgi?id=221096 Link: https://github.com/openwrt/mt76/issues/927 Reported-by: Ryan Gilbert <xelnaga@gmail.com> Signed-off-by: Javier Tia <floss@jetm.me> Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>