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Message-ID: <713b1d0333eb2f12e63bc8a7b8f423e1240abae0.camel@iki.fi>
Subject: Re: [PATCH v2 0/5] Bluetooth: add TX timestamping for ISO/SCO/L2CAP
From: Pauli Virtanen <pav@iki.fi>
To: linux-bluetooth@vger.kernel.org
Cc: Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Date: Fri, 22 Mar 2024 18:56:31 +0200
In-Reply-To: <cover.1710440392.git.pav@iki.fi>
References: <cover.1710440392.git.pav@iki.fi>
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Hi Luiz,

to, 2024-03-14 kello 20:20 +0200, Pauli Virtanen kirjoitti:
> Add support for TX timestamping in ISO/SCO/L2CAP sockets.
>=20
> These patches allow fixing / working around controller(?) issue where
> two ISO streams in same group get desynchronized. It also gives user
> applications the best latency information as available to kernel.
>=20
> Also add sockopt BT_NO_ERRQUEUE_POLL to optionally disable POLLERR
> wakeup on TX timestamp arrival, which is mainly a nuisance in the use
> case here.  The alternative to this seems be to deal with the POLLERR
> wakeups in BlueZ side, but this seems hard as it's always enabled in
> poll() flags so not clear if anything else than polling at regular
> intervals can be done there.

Any suggestions what the plan here should be?

The suggestions so far:

1. Socket TX timestamping & deal with POLLERR in BlueZ

2. Socket TX timestamping & disable POLLERR via setsockopt

3. Some custom latency reporting mechanism


> Pipewire side:
> https://gitlab.freedesktop.org/pvir/pipewire/-/commits/iso-ts-test2
>=20
> With this change, https://github.com/bluez/bluez/issues/515 is more or
> less fixed, and the sound server can figure out the total latency to
> audio rendering (tx latency + transport latency + presentation delay).
>=20
> For ISO, we can later use LE Read ISO TX Sync to provide hardware
> timestamps, but this requires figuring out the sequence number
> synchronization first.
>=20
> v2:
> - Rename *tx_comp* -> *tx*
> - Add hci_send_conn_frame() and handle all link types
> - Add SCO timestamping. Deal with no flow control -> no Num_Comp_* events
> - Handle HCI_FLOW_CTL_MODE_BLOCK_BASED
> - Add BT_NO_ERRQUEUE_POLL
>=20
> Pauli Virtanen (5):
>   Bluetooth: add support for skb TX timestamping
>   Bluetooth: ISO: add TX timestamping
>   Bluetooth: L2CAP: add TX timestamping
>   Bluetooth: SCO: add TX timestamping
>   Bluetooth: add BT_NO_ERRQUEUE_POLL socket option
>=20
>  include/net/bluetooth/bluetooth.h |  10 ++-
>  include/net/bluetooth/hci_core.h  |  12 ++++
>  include/net/bluetooth/l2cap.h     |   3 +-
>  net/bluetooth/6lowpan.c           |   2 +-
>  net/bluetooth/af_bluetooth.c      |  72 ++++++++++++++++++-
>  net/bluetooth/hci_conn.c          | 111 ++++++++++++++++++++++++++++++
>  net/bluetooth/hci_core.c          |  19 +++--
>  net/bluetooth/hci_event.c         |  11 ++-
>  net/bluetooth/iso.c               |  32 ++++++---
>  net/bluetooth/l2cap_core.c        |  11 ++-
>  net/bluetooth/l2cap_sock.c        |  23 +++++--
>  net/bluetooth/sco.c               |  27 ++++++--
>  net/bluetooth/smp.c               |   2 +-
>  13 files changed, 303 insertions(+), 32 deletions(-)
>=20

--=20
Pauli Virtanen