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

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Message-ID: <CAL+tcoAXCbhNG2-Pdd7C3iJD9h=GvM1PNstyMJXO8KE7XKAzDw@mail.gmail.com>
Date: Sat, 5 Jul 2025 09:59:18 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: yang.li@...ogic.com
Cc: 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>, 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 Yang,

On Fri, Jul 4, 2025 at 1:36 PM Yang Li via B4 Relay
<devnull+yang.li.amlogic.com@...nel.org> wrote:
>
> 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.
> +                        */

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 :)

> +                       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.

> +                       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.

Thanks,
Jason