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

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Message-ID: <11d1bf49-c417-b3cd-38e3-0f7d14dd8b12@intel.com>
Date:   Thu, 13 Apr 2023 09:54:59 -0700
From:   Jacob Keller <jacob.e.keller@...el.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>
CC:     <intel-wired-lan@...ts.osuosl.org>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <bpf@...r.kernel.org>,
        <xdp-hints@...-project.net>, <stable@...r.kernel.org>
Subject: Re: [PATCH net 1/1] igc: read before write to SRRCTL register



On 4/13/2023 8:12 AM, 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 = 1677762212.590696226
> 
> 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>