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

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

Hi,
> [ EXTERNAL EMAIL ]
>
> Hi,
>
> pe, 2025-07-04 kello 13:36 +0800, Yang Li via B4 Relay kirjoitti:
>> 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.
>> +                      */
>> +                     struct skb_shared_hwtstamps *hwts = skb_hwtstamps(skb);
>> +                     if (hwts)
> In addition to the moving variable on top, the null check is spurious
> as skb_hwtstamps is never NULL (driver/net/* do not check it either).
>
> Did you test this with SOF_TIMESTAMPING_RX_HARDWARE in userspace?
> Pipewire does not try to get HW timestamps right now.
>
> Would be good to also add some tests in bluez/tools/iso-tester.c
> although this needs some extension to the emulator/* to support
> timestamps properly.


Yes, here is the patch and log based on testing with Pipewire:

diff --git a/spa/plugins/bluez5/media-source.c 
b/spa/plugins/bluez5/media-source.c
index 2fe08b8..10e9378 100644
--- a/spa/plugins/bluez5/media-source.c
+++ b/spa/plugins/bluez5/media-source.c
@@ -407,7 +413,7 @@ static int32_t read_data(struct impl *this) {
         struct msghdr msg = {0};
         struct iovec iov;
         char control[128];
-       struct timespec *ts = NULL;
+       struct scm_timestamping *ts = NULL;

         iov.iov_base = this->buffer_read;
         iov.iov_len = b_size;
@@ -439,12 +445,14 @@ again:
         struct cmsghdr *cmsg;
         for (cmsg = CMSG_FIRSTHDR(&msg); cmsg != NULL; cmsg = 
CMSG_NXTHDR(&msg, cmsg)) {
  #ifdef SCM_TIMESTAMPING
                 /* Check for timestamp */
+               if (cmsg->cmsg_level == SOL_SOCKET && cmsg->cmsg_type == 
SCM_TIMESTAMPING) {
+                       ts = (struct scm_timestamping *)CMSG_DATA(cmsg);
+                       spa_log_error(this->log, "%p: received timestamp 
%ld.%09ld",
+                                       this, ts->ts[2].tv_sec, 
ts->ts[2].tv_nsec);
                         break;
                 }
  #endif

  @@ -726,9 +734,9 @@ static int transport_start(struct impl *this)
         if (setsockopt(this->fd, SOL_SOCKET, SO_PRIORITY, &val, 
sizeof(val)) < 0)
                 spa_log_warn(this->log, "SO_PRIORITY failed: %m");

+       val = SOF_TIMESTAMPING_RX_HARDWARE | SOF_TIMESTAMPING_RAW_HARDWARE;
+       if (setsockopt(this->fd, SOL_SOCKET, SO_TIMESTAMPING, &val, 
sizeof(val)) < 0) {
+               spa_log_warn(this->log, "SO_TIMESTAMPING failed: %m");
                 /* don't fail if timestamping is not supported */
         }

trace log：

read_data: 0x1e78d68: received timestamp 7681.972000000
read_data: 0x1e95000: received timestamp 7681.972000000
read_data: 0x1e78d68: received timestamp 7691.972000000
read_data: 0x1e95000: received timestamp 7691.972000000
read_data: 0x1e78d68: received timestamp 7701.972000000
read_data: 0x1e95000: received timestamp 7701.972000000
read_data: 0x1e78d68: received timestamp 7711.972000000
read_data: 0x1e95000: received timestamp 7711.972000000
read_data: 0x1e78d68: received timestamp 7721.972000000
read_data: 0x1e95000: received timestamp 7721.972000000
read_data: 0x1e78d68: received timestamp 7731.972000000

>
>> +                             hwts->hwtstamp = us_to_ktime(le32_to_cpu(hdr->ts));
>> +
>>                        len = __le16_to_cpu(hdr->slen);
>>                } else {
>>                        struct hci_iso_data_hdr *hdr;
>>
>> ---
>> base-commit: 3bc46213b81278f3a9df0324768e152de71eb9fe
>> change-id: 20250421-iso_ts-c82a300ae784
>>
>> Best regards,
> --
> Pauli Virtanen