linux-kernel - Re: [Intel-wired-lan] [PATCH net v3 1/1] igc: read before write to SRRCTL register

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Message-ID: <499598fd-05fc-e3bc-be85-d74b47a0b46c@linux.intel.com>
Date:   Sun, 30 Apr 2023 08:05:57 +0300
From:   "naamax.meir" <naamax.meir@...ux.intel.com>
To:     Song Yoong Siang <yoong.siang.song@...el.com>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Tony Nguyen <anthony.l.nguyen@...el.com>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Vedang Patel <vedang.patel@...el.com>,
        Jithu Joseph <jithu.joseph@...el.com>,
        Andre Guedes <andre.guedes@...el.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Stanislav Fomichev <sdf@...gle.com>,
        Jacob Keller <jacob.e.keller@...el.com>,
        David Laight <David.Laight@...LAB.COM>
Cc:     xdp-hints@...-project.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        intel-wired-lan@...ts.osuosl.org, bpf@...r.kernel.org
Subject: Re: [Intel-wired-lan] [PATCH net v3 1/1] igc: read before write to
 SRRCTL register

On 4/14/2023 18:49, Song Yoong Siang wrote:
> igc_configure_rx_ring() function will be called as part of XDP program
> setup. If Rx hardware timestamp is enabled prio to XDP program setup,
> this timestamp enablement will be overwritten when buffer size is
> written into SRRCTL register.
> 
> Thus, this commit read the register value before write to SRRCTL
> register. This commit is tested by using xdp_hw_metadata bpf selftest
> tool. The tool enables Rx hardware timestamp and then attach XDP program
> to igc driver. It will display hardware timestamp of UDP packet with
> port number 9092. Below are detail of test steps and results.
> 
> Command on DUT:
>    sudo ./xdp_hw_metadata <interface name>
> 
> Command on Link Partner:
>    echo -n skb | nc -u -q1 <destination IPv4 addr> 9092
> 
> Result before this patch:
>    skb hwtstamp is not found!
> 
> Result after this patch:
>    found skb hwtstamp = 1677800973.642836757
> 
> Optionally, read PHC to confirm the values obtained are almost the same:
> Command:
>    sudo ./testptp -d /dev/ptp0 -g
> Result:
>    clock time: 1677800973.913598978 or Fri Mar  3 07:49:33 2023
> 
> Fixes: fc9df2a0b520 ("igc: Enable RX via AF_XDP zero-copy")
> Cc: <stable@...r.kernel.org> # 5.14+
> Signed-off-by: Song Yoong Siang <yoong.siang.song@...el.com>
> Reviewed-by: Jacob Keller <jacob.e.keller@...el.com>
> Reviewed-by: Jesper Dangaard Brouer <brouer@...hat.com>
> ---
> v2 -> v3: Refactor SRRCTL definitions to more human readable definitions
> v1 -> v2: Fix indention
> ---
>   drivers/net/ethernet/intel/igc/igc_base.h | 11 ++++++++---
>   drivers/net/ethernet/intel/igc/igc_main.c |  7 +++++--
>   2 files changed, 13 insertions(+), 5 deletions(-)

Tested-by: Naama Meir <naamax.meir@...ux.intel.com>