Re: [PATCH] Bluetooth: hci_event: Add support for handling LE BIG Sync Lost event

[Yang Li <yang.li@amlogic.com>]

在 2025/6/25 1:17, Luiz Augusto von Dentz 写道:
> [ EXTERNAL EMAIL ]
>
> Hi,
>
> On Tue, Jun 24, 2025 at 12:56 PM Luiz Augusto von Dentz
> <luiz.dentz@gmail.com> wrote:
>> Hi,
>>
>> On Tue, Jun 24, 2025 at 1:20 AM Yang Li via B4 Relay
>> <devnull+yang.li.amlogic.com@kernel.org> wrote:
>>> From: Yang Li <yang.li@amlogic.com>
>>>
>>> When the BIS source stops, the controller sends an LE BIG Sync Lost
>>> event (subevent 0x1E). Currently, this event is not handled, causing
>>> the BIS stream to remain active in BlueZ and preventing recovery.
>>>
>>> Signed-off-by: Yang Li <yang.li@amlogic.com>
>>> ---
>>>   include/net/bluetooth/hci.h |  6 ++++++
>>>   net/bluetooth/hci_event.c   | 23 +++++++++++++++++++++++
>>>   2 files changed, 29 insertions(+)
>>>
>>> diff --git a/include/net/bluetooth/hci.h b/include/net/bluetooth/hci.h
>>> index 82cbd54443ac..48389a64accb 100644
>>> --- a/include/net/bluetooth/hci.h
>>> +++ b/include/net/bluetooth/hci.h
>>> @@ -2849,6 +2849,12 @@ struct hci_evt_le_big_sync_estabilished {
>>>          __le16  bis[];
>>>   } __packed;
>>>
>>> +#define HCI_EVT_LE_BIG_SYNC_LOST 0x1e
>>> +struct hci_evt_le_big_sync_lost {
>>> +       __u8    handle;
>>> +       __u8    reason;
>>> +} __packed;
>>> +
>>>   #define HCI_EVT_LE_BIG_INFO_ADV_REPORT 0x22
>>>   struct hci_evt_le_big_info_adv_report {
>>>          __le16  sync_handle;
>>> diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
>>> index 66052d6aaa1d..730deaf1851f 100644
>>> --- a/net/bluetooth/hci_event.c
>>> +++ b/net/bluetooth/hci_event.c
>>> @@ -7026,6 +7026,24 @@ static void hci_le_big_sync_established_evt(struct hci_dev *hdev, void *data,
>>>          hci_dev_unlock(hdev);
>>>   }
>>>
>>> +static void hci_le_big_sync_lost_evt(struct hci_dev *hdev, void *data,
>>> +                                           struct sk_buff *skb)
>>> +{
>>> +       struct hci_evt_le_big_sync_lost *ev = data;
>>> +       struct hci_conn *conn;
>>> +
>>> +       bt_dev_dbg(hdev, "BIG Sync Lost: big_handle 0x%2.2x", ev->handle);
>>> +
>>> +       hci_dev_lock(hdev);
>>> +
>>> +       list_for_each_entry(conn, &hdev->conn_hash.list, list) {
>>> +               if (test_bit(HCI_CONN_BIG_SYNC, &conn->flags))
>>> +                       hci_disconn_cfm(conn, HCI_ERROR_REMOTE_USER_TERM);
>>> +       }
>> Let's start with the obvious problems:
>>
>> 1. This does not use the handle, instead it disconnects all the
>> connections with HCI_CONN_BIG_SYNC
>> 2. It doesn't use the reason either
>> 3. hci_disconnect_cfm should be followed with hci_conn_del to free the hci_conn
>>
>> So this does tell me you don't fully understand what you are doing, I
>> hope I am not dealing with some AI generated code otherwise I would
>> just do it myself.


Thank you for pointing that out. I overlooked these three issues, and 
they will be fixed in the next revision.

> Btw, the spec does says the controller shall cleanup the connection
> handle and data path:
>
> When the HCI_LE_BIG_Sync_Lost event occurs, the Controller shall
> remove the connection handle(s) and data paths of all BIS(s) in the
> BIG with which the Controller was synchronized.
>
> I wonder if that shall be interpreted as no HCI_Disconnection_Complete
> shall be generated or what, also we might need to implement this into
> BlueZ emulator in order to replicate this in our CI tests.
>
> It seems we are not sending anything to the remote devices when
> receiving BT_HCI_CMD_LE_BIG_TERM_SYNC:
>
> https://github.com/bluez/bluez/blob/master/emulator/btdev.c#L6661


When the HCI_LE_BIG_Sync_Lost event occurs, there is no accompanying 
HCI_Disconnection_Complete event.

However, in the patch submitted to BlueZ, it is described that the 
HCI_Disconnection_Complete event will be reported when the CIS link is 
disconnected.

https://lore.kernel.org/all/20250624-bap_for_big_sync_lost-v1-1-0df90a0f55d0@amlogic.com/

I believe that the HCI_LE_BIG_Sync_Lost event is triggered passively by 
the controller when it is unable to synchronize with the BIS stream.
This may occur for various reasons — such as the BIS source pausing 
transmission, the device moving out of range, or interference.
This behavior is different from the host actively issuing the 
LE_BIG_Terminate_Sync command.

In actual products, this condition can be communicated back to the phone 
(Assistant) via the Broadcast Receive State characteristic defined in BASS.
However, in a simulator or test environment, there's often not much that 
needs to be done when sending LE_BIG_Terminate_Sync command.

>
>>> +       hci_dev_unlock(hdev);
>>> +}
>>> +
>>>   static void hci_le_big_info_adv_report_evt(struct hci_dev *hdev, void *data,
>>>                                             struct sk_buff *skb)
>>>   {
>>> @@ -7149,6 +7167,11 @@ static const struct hci_le_ev {
>>>                       hci_le_big_sync_established_evt,
>>>                       sizeof(struct hci_evt_le_big_sync_estabilished),
>>>                       HCI_MAX_EVENT_SIZE),
>>> +       /* [0x1e = HCI_EVT_LE_BIG_SYNC_LOST] */
>>> +       HCI_LE_EV_VL(HCI_EVT_LE_BIG_SYNC_LOST,
>>> +                    hci_le_big_sync_lost_evt,
>>> +                    sizeof(struct hci_evt_le_big_sync_lost),
>>> +                    HCI_MAX_EVENT_SIZE),
>>>          /* [0x22 = HCI_EVT_LE_BIG_INFO_ADV_REPORT] */
>>>          HCI_LE_EV_VL(HCI_EVT_LE_BIG_INFO_ADV_REPORT,
>>>                       hci_le_big_info_adv_report_evt,
>>>
>>> ---
>>> base-commit: bd35cd12d915bc410c721ba28afcada16f0ebd16
>>> change-id: 20250612-handle_big_sync_lost_event-4c7dc64390a2
>>>
>>> Best regards,
>>> --
>>> Yang Li <yang.li@amlogic.com>
>>>
>>>
>>
>> --
>> Luiz Augusto von Dentz
>
>
> --
> Luiz Augusto von Dentz