netdev - Re: [PATCH net v3 1/1] igc: read before write to SRRCTL register

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Message-ID: <e7b9cb2c-1c18-7354-8d33-a924b5ae1d5b@redhat.com>
Date:   Mon, 17 Apr 2023 16:24:34 +0200
From:   Jesper Dangaard Brouer <jbrouer@...hat.com>
To:     Song Yoong Siang <yoong.siang.song@...el.com>,
        "Bezdeka, Florian" <florian.bezdeka@...mens.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>,
        Stanislav Fomichev <sdf@...gle.com>,
        Jacob Keller <jacob.e.keller@...el.com>,
        David Laight <David.Laight@...LAB.COM>
Cc:     brouer@...hat.com, 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 v3 1/1] igc: read before write to SRRCTL register


On 14/04/2023 22.05, Jesper Dangaard Brouer wrote:
>  
> On 14/04/2023 17.49, 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.
>>
[...]
>>
>> 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>
>> ---
> 
> LGTM, thank for the adjustments :-)
> 
> Acked-by: Jesper Dangaard Brouer <brouer@...hat.com>
> 

Tested-by: Jesper Dangaard Brouer <brouer@...hat.com>

I can confirm that this patch fix the issue I experienced with igc.

This patch clearly fixes a bug in igc when writing the SRRCTL register.
(as bit 30 in register is "Timestamp Received Packet" which got cleared 
before).

Florian might have found another bug around RX timestamps, but this
patch should be safe and sane to apply as is.

>> 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(-)