netdev - Re: [PATCH v3] Bluetooth: ISO: Support SCM

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Message-ID: <bebb44579ed8379a0d69a2f2793a70471b08ea91.camel@iki.fi>
Date: Sat, 05 Jul 2025 23:39:58 +0300
From: Pauli Virtanen <pav@....fi>
To: yang.li@...ogic.com, Marcel Holtmann <marcel@...tmann.org>, Johan
 Hedberg	 <johan.hedberg@...il.com>, Luiz Augusto von Dentz
 <luiz.dentz@...il.com>,  "David S. Miller" <davem@...emloft.net>, Eric
 Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo
 Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>
Cc: linux-bluetooth@...r.kernel.org, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] Bluetooth: ISO: Support SCM_TIMESTAMPING for ISO TS

Hi,

pe, 2025-07-04 kello 13:36 +0800, Yang Li via B4 Relay kirjoitti:
> From: Yang Li <yang.li@...ogic.com>
> 
> User-space applications (e.g., PipeWire) depend on
> ISO-formatted timestamps for precise audio sync.
> 
> Signed-off-by: Yang Li <yang.li@...ogic.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.

> +				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