Re: [PATCH v4] Bluetooth: ISO: Support SCM_TIMESTAMPING for ISO TS

[Pauli Virtanen <pav@iki.fi>]

Hi Yang,

ma, 2025-07-07 kello 10:38 +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.
> 
> The ISO ts is based on the controller’s clock domain,
> so hardware timestamping (hwtimestamp) must be used.
> 
> Ref: Documentation/networking/timestamping.rst,
> section 3.1 Hardware Timestamping.
> 
> Signed-off-by: Yang Li <yang.li@amlogic.com>
> ---
> Changes in v4:
> - Optimizing the code
> - Link to v3: https://lore.kernel.org/r/20250704-iso_ts-v3-1-2328bc602961@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 | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/net/bluetooth/iso.c b/net/bluetooth/iso.c
> index fc22782cbeeb..677144bb6b94 100644
> --- a/net/bluetooth/iso.c
> +++ b/net/bluetooth/iso.c
> @@ -2278,6 +2278,7 @@ static void iso_disconn_cfm(struct hci_conn *hcon, __u8 reason)
>  void iso_recv(struct hci_conn *hcon, struct sk_buff *skb, u16 flags)
>  {
>  	struct iso_conn *conn = hcon->iso_data;
> +	struct skb_shared_hwtstamps *hwts;
>  	__u16 pb, ts, len;
>  
>  	if (!conn)
> @@ -2301,13 +2302,16 @@ 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;
>  			}
>  
> +			/*  Record the timestamp to skb*/
> +			hwts = skb_hwtstamps(skb);
> +			hwts->hwtstamp = us_to_ktime(le32_to_cpu(hdr->ts));

Several lines below there is 

	conn->rx_skb = bt_skb_alloc(len, GFP_KERNEL);
	skb_copy_from_linear_data(skb, skb_put(conn->rx_skb, skb-
>len),
        	                                  skb->len);

so timestamp should be copied explicitly also into conn->rx_skb,
otherwise it gets lost when you have ACL-fragmented ISO packets.

It could also be useful to write a simple test case that extracts the
timestamp from CMSG, see for example how it was done for BT_PKT_SEQNUM:
https://lore.kernel.org/linux-bluetooth/b98b7691e4ba06550bb8f275cad0635bc9e4e8d2.1752511478.git.pav@iki.fi/
bthost_send_iso() can take ts=true and some timestamp value.

> +
>  			len = __le16_to_cpu(hdr->slen);
>  		} else {
>  			struct hci_iso_data_hdr *hdr;
> 
> ---
> base-commit: b8db3a9d4daeb7ff6a56c605ad6eca24e4da78ed
> change-id: 20250421-iso_ts-c82a300ae784
> 
> Best regards,

-- 
Pauli Virtanen