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

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Date:   Fri, 01 Dec 2023 10:26:51 -0500
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Jesper Dangaard Brouer <hawk@...nel.org>,
        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

Jesper Dangaard Brouer wrote:
> 
> 
> 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

Good point Jesper.

Can we also explicitly document what the type of the field is?
Nanoseconds against the NIC hardware clock, it sounds like.

We have some experience with this, too. Something needs to do the
conversion from host clock to NIC clock. It is not sufficent to just
assume that the host clock is synced against the NIC clock by PTP.