linux-kernel - [PATCH v2 1/1] Bluetooth: btusb: Reclassify Qualcomm WCN6855 debug packets

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Message-ID: <20251007153315.72565-1-pascal.giard@etsmtl.ca>
Date: Tue,  7 Oct 2025 11:33:15 -0400
From: Pascal Giard <evilynux@...il.com>
To: marcel@...tmann.org,
	luiz.dentz@...il.com
Cc: linux-bluetooth@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Pascal Giard <pascal.giard@...mtl.ca>
Subject: [PATCH v2 1/1] Bluetooth: btusb: Reclassify Qualcomm WCN6855 debug packets

Some Qualcomm Bluetooth controllers, e.g., QCNFA765 with WCN6855
chip, send debug packets as ACL frames with header 0x2EDC.
The kernel misinterprets these as malformed ACL packets, causing
repeated errors:

  Bluetooth: hci0: ACL packet for unknown connection handle 3804

This can occur hundreds of times per minute, greatly cluttering logs.
On my computer, I am observing approximately 7 messages per second
when streaming audio to a speaker.

For Qualcomm controllers exchanging over UART, hci_qca.c already
filters out these debug packets. This patch is for controllers
not going through UART, but USB.

This patch uses the classify_pkt_type callback to reclassify the
packets with handle 0x2EDC as HCI_DIAG_PKT before they reach the
HCI layer. This change is only applied to Qualcomm devices marked
as BTUSB_QCA_WCN6855.

Tested on: Thinkpad T14 gen2 (AMD) with QCNFA765 (0489:E0D0)
Signed-off-by: Pascal Giard <pascal.giard@...mtl.ca>
---
Changes in v2:
- Address reviewer feedback about 0x2EDC being a valid HCI handle
- Use classify_pkt_type callback instead of filtering in recv_acl
- Only apply to devices with BTUSB_QCA_WCN6855 quirk
---
 drivers/bluetooth/btusb.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/bluetooth/btusb.c b/drivers/bluetooth/btusb.c
index 5e9ebf0c5312..256179ace853 100644
--- a/drivers/bluetooth/btusb.c
+++ b/drivers/bluetooth/btusb.c
@@ -1131,6 +1131,24 @@ static void btusb_qca_reset(struct hci_dev *hdev)
 	btusb_reset(hdev);
 }
 
+static u8 btusb_classify_qca_pkt_type(struct hci_dev *hdev, struct sk_buff *skb)
+{
+	/* Some Qualcomm controllers, e.g., QCNFA765 with WCN6855 chip, send debug
+	 * packets as ACL frames with connection handle 0x2EDC. These are not real
+	 * ACL packets and should be reclassified as HCI_DIAG_PKT to prevent
+	 * "ACL packet for unknown connection handle 3804" errors.
+	 */
+	if (skb->len >= 2) {
+		u16 handle = get_unaligned_le16(skb->data);
+
+		if (handle == 0x2EDC)
+			return HCI_DIAG_PKT;
+	}
+
+	/* Use default packet type for other packets */
+	return hci_skb_pkt_type(skb);
+}
+
 static inline void btusb_free_frags(struct btusb_data *data)
 {
 	unsigned long flags;
@@ -4201,6 +4219,7 @@ static int btusb_probe(struct usb_interface *intf,
 		data->recv_acl = btusb_recv_acl_qca;
 		hci_devcd_register(hdev, btusb_coredump_qca, btusb_dump_hdr_qca, NULL);
 		data->setup_on_usb = btusb_setup_qca;
+		hdev->classify_pkt_type = btusb_classify_qca_pkt_type;
 		hdev->shutdown = btusb_shutdown_qca;
 		hdev->set_bdaddr = btusb_set_bdaddr_wcn6855;
 		hdev->reset = btusb_qca_reset;
-- 
2.51.0