netdev - Re: [PATCH bpf-next v2 2/3] net: stmmac: Add txtime support to XDP ZC

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Date: Fri, 1 Dec 2023 16:02:22 +0100
From: Jesper Dangaard Brouer <hawk@...nel.org>
To: Song Yoong Siang <yoong.siang.song@...el.com>,
 "David S . Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, Jonathan Corbet <corbet@....net>,
 Bjorn Topel <bjorn@...nel.org>, Magnus Karlsson <magnus.karlsson@...el.com>,
 Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
 Jonathan Lemon <jonathan.lemon@...il.com>,
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
 John Fastabend <john.fastabend@...il.com>,
 Stanislav Fomichev <sdf@...gle.com>, Lorenzo Bianconi <lorenzo@...nel.org>,
 Tariq Toukan <tariqt@...dia.com>, Willem de Bruijn <willemb@...gle.com>,
 Maxime Coquelin <mcoquelin.stm32@...il.com>,
 Andrii Nakryiko <andrii@...nel.org>, Mykola Lysenko <mykolal@...com>,
 Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>,
 Yonghong Song <yonghong.song@...ux.dev>, KP Singh <kpsingh@...nel.org>,
 Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
 Shuah Khan <shuah@...nel.org>,
 Alexandre Torgue <alexandre.torgue@...s.st.com>,
 Jose Abreu <joabreu@...opsys.com>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-doc@...r.kernel.org, bpf@...r.kernel.org, xdp-hints@...-project.net,
 linux-stm32@...md-mailman.stormreply.com,
 linux-arm-kernel@...ts.infradead.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH bpf-next v2 2/3] net: stmmac: Add txtime support to XDP ZC

On 12/1/23 07:24, Song Yoong Siang wrote:
> This patch enables txtime support to XDP zero copy via XDP Tx
> metadata framework.
> 
> Signed-off-by: Song Yoong Siang<yoong.siang.song@...el.com>
> ---
>   drivers/net/ethernet/stmicro/stmmac/stmmac.h      |  2 ++
>   drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 13 +++++++++++++
>   2 files changed, 15 insertions(+)

I think we need to see other drivers using this new feature to evaluate
if API is sane.

I suggest implementing this for igc driver (chip i225) and also for igb
(i210 chip) that both support this kind of LaunchTime feature in HW.

The API and stmmac driver takes a u64 as time.
I'm wondering how this applies to i210 that[1] have 25-bit for
LaunchTime (with 32 nanosec granularity) limiting LaunchTime max 0.5
second into the future.
And i225 that [1] have 30-bit max 1 second into the future.

[1] 
https://github.com/xdp-project/xdp-project/blob/master/areas/tsn/code01_follow_qdisc_TSN_offload.org