linux-kernel - Re: [PATCH] Bluetooth: Add filter for Qualcomm debug packets

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Message-ID: <CABBYNZJVUoVnJPdOXARvk7T_9EsvomJ_oe_ZZ_QZMTQBVjNDHw@mail.gmail.com>
Date: Mon, 6 Oct 2025 13:21:07 -0400
From: Luiz Augusto von Dentz <luiz.dentz@...il.com>
To: Pascal Giard <evilynux@...il.com>
Cc: marcel@...tmann.org, linux-bluetooth@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Pascal Giard <pascal.giard@...mtl.ca>
Subject: Re: [PATCH] Bluetooth: Add filter for Qualcomm debug packets

Hi Pascal,

On Fri, Oct 3, 2025 at 4:59 PM Pascal Giard <evilynux@...il.com> wrote:
>
> Some Qualcomm Bluetooth controllers, e.g., QCNFA765 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 filters these packets in btusb_recv_acl() before they reach
> the HCI layer, redirecting them to hci_recv_diag().
>
> Tested on: Thinkpad T14 gen2 (AMD) with QCNFA765, kernel 6.16.9
>
> Signed-off-by: Pascal Giard <pascal.giard@...mtl.ca>
> ---
>  drivers/bluetooth/btusb.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/drivers/bluetooth/btusb.c b/drivers/bluetooth/btusb.c
> index 5e9ebf0c5312..900400646315 100644
> --- a/drivers/bluetooth/btusb.c
> +++ b/drivers/bluetooth/btusb.c
> @@ -68,6 +68,9 @@ static struct usb_driver btusb_driver;
>  #define BTUSB_ACTIONS_SEMI             BIT(27)
>  #define BTUSB_BARROT                   BIT(28)
>
> +/* Qualcomm firmware debug packets header */
> +#define QCA_DEBUG_HEADER       0x2EDC
> +
>  static const struct usb_device_id btusb_table[] = {
>         /* Generic Bluetooth USB device */
>         { USB_DEVICE_INFO(0xe0, 0x01, 0x01) },
> @@ -1229,6 +1232,12 @@ static int btusb_recv_intr(struct btusb_data *data, void *buffer, int count)
>
>  static int btusb_recv_acl(struct btusb_data *data, struct sk_buff *skb)
>  {
> +       /* Drop QCA firmware debug packets sent as ACL frames */
> +       if (skb->len >= 2) {
> +               if (get_unaligned_le16(skb->data) == QCA_DEBUG_HEADER)
> +                       return hci_recv_diag(data->hdev, skb);
> +       }

Well it turns out that handle 0x2EDC is actually a valid handle, so we
can't just reclassify these packets just because Qualcomm thinks that
it could reserve it for its own, so this needs to be using
classify_pkt_type to reclassify the packets to the handle 0x2EDC to
HCI_DIAG_PKT for the models affected.

>         /* Only queue ACL packet if intr_interval is set as it means
>          * force_poll_sync has been enabled.
>          */
> --
> 2.51.0
>


-- 
Luiz Augusto von Dentz