Re: [PATCH v3] Bluetooth: ISO: Support SCM_TIMESTAMPING for ISO TS

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

Hi Jason,
> [ EXTERNAL EMAIL ]
>
> Hi Yang,
>
> On Fri, Jul 4, 2025 at 1:36 PM Yang Li via B4 Relay
> <devnull+yang.li.amlogic.com@kernel.org> wrote:
>> From: Yang Li <yang.li@amlogic.com>
>>
>> User-space applications (e.g., PipeWire) depend on
>> ISO-formatted timestamps for precise audio sync.
>>
>> Signed-off-by: Yang Li <yang.li@amlogic.com>
>> ---
>> Changes in v3:
>> - Change to use hwtimestamp
>> - Link to v2: https://lore.kernel.org/r/20250702-iso_ts-v2-1-723d199c8068@amlogic.com
>>
>> Changes in v2:
>> - Support SOCK_RCVTSTAMPNS via CMSG for ISO sockets
>> - Link to v1: https://lore.kernel.org/r/20250429-iso_ts-v1-1-e586f30de6cb@amlogic.com
>> ---
>>   net/bluetooth/iso.c | 10 +++++++++-
>>   1 file changed, 9 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/bluetooth/iso.c b/net/bluetooth/iso.c
>> index fc22782cbeeb..67ff355167d8 100644
>> --- a/net/bluetooth/iso.c
>> +++ b/net/bluetooth/iso.c
>> @@ -2301,13 +2301,21 @@ void iso_recv(struct hci_conn *hcon, struct sk_buff *skb, u16 flags)
>>                  if (ts) {
>>                          struct hci_iso_ts_data_hdr *hdr;
>>
>> -                       /* TODO: add timestamp to the packet? */
>>                          hdr = skb_pull_data(skb, HCI_ISO_TS_DATA_HDR_SIZE);
>>                          if (!hdr) {
>>                                  BT_ERR("Frame is too short (len %d)", skb->len);
>>                                  goto drop;
>>                          }
>>
>> +                       /* The ISO ts is based on the controller’s clock domain,
>> +                        * so hardware timestamping (hwtimestamp) must be used.
>> +                        * Ref: Documentation/networking/timestamping.rst,
>> +                        * chapter 3.1 Hardware Timestamping.
>> +                        */
> I think the above comment is not necessary as it's a common usage for
> all kinds of drivers. If you reckon the information could be helpful,
> then you could clarify it in the commit message :)


Okay, I got it.

>
>> +                       struct skb_shared_hwtstamps *hwts = skb_hwtstamps(skb);
> The above line should be moved underneath the 'if (ts) {' line because
> we need to group all the declarations altogether at the beginning.


Yes, I will do.

>
>> +                       if (hwts)
>> +                               hwts->hwtstamp = us_to_ktime(le32_to_cpu(hdr->ts));
>> +
> I'm definitely not a bluetooth expert, so I'm here only to check the
> timestamping usage. According to your prior v2 patch, the
> reader/receiver to turn on the timestamping feature is implemented in
> PipeWire? If so, so far the kernel part looks good to me.


Yes, please reference reply:

https://lore.kernel.org/all/df9f6977-0d63-41b3-8d9b-c3a293ed78ec@amlogic.com/


>
> Thanks,
> Jason