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

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Date:   Fri, 14 Apr 2023 01:36:13 +0000
From:   "Song, Yoong Siang" <yoong.siang.song@...el.com>
To:     Jesper Dangaard Brouer <jbrouer@...hat.com>,
        "Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
        "Nguyen, Anthony L" <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>,
        "Fijalkowski, Maciej" <maciej.fijalkowski@...el.com>,
        Vedang Patel <vedang.patel@...el.com>,
        "Joseph, Jithu" <jithu.joseph@...el.com>,
        Andre Guedes <andre.guedes@...el.com>,
        Stanislav Fomichev <sdf@...gle.com>
CC:     "Brouer, Jesper" <brouer@...hat.com>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "xdp-hints@...-project.net" <xdp-hints@...-project.net>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: RE: [PATCH net 1/1] igc: read before write to SRRCTL register

On Friday, April 14, 2023 3:06 AM , Jesper Dangaard Brouer <jbrouer@...hat.com> wrote:
>On 13/04/2023 17.12, 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.
>[...]
>> diff --git a/drivers/net/ethernet/intel/igc/igc_base.h
>> b/drivers/net/ethernet/intel/igc/igc_base.h
>> index 7a992befca24..b95007d51d13 100644
>> --- a/drivers/net/ethernet/intel/igc/igc_base.h
>> +++ b/drivers/net/ethernet/intel/igc/igc_base.h
>> @@ -87,8 +87,11 @@ union igc_adv_rx_desc {
>>   #define IGC_RXDCTL_SWFLUSH		0x04000000 /* Receive Software Flush */
>>
>>   /* SRRCTL bit definitions */
>> -#define IGC_SRRCTL_BSIZEPKT_SHIFT		10 /* Shift _right_ */
>> -#define IGC_SRRCTL_BSIZEHDRSIZE_SHIFT		2  /* Shift _left_ */
>> +#define IGC_SRRCTL_BSIZEPKT_MASK	GENMASK(6, 0)
>> +#define IGC_SRRCTL_BSIZEPKT_SHIFT	10 /* Shift _right_ */
>> +#define IGC_SRRCTL_BSIZEHDRSIZE_MASK	GENMASK(13, 8)
>> +#define IGC_SRRCTL_BSIZEHDRSIZE_SHIFT	2  /* Shift _left_ */
>> +#define IGC_SRRCTL_DESCTYPE_MASK	GENMASK(27, 25)
>>   #define IGC_SRRCTL_DESCTYPE_ADV_ONEBUF	0x02000000
>>
>>   #endif /* _IGC_BASE_H */
>> diff --git a/drivers/net/ethernet/intel/igc/igc_main.c
>> b/drivers/net/ethernet/intel/igc/igc_main.c
>> index 25fc6c65209b..de7b21c2ccd6 100644
>> --- a/drivers/net/ethernet/intel/igc/igc_main.c
>> +++ b/drivers/net/ethernet/intel/igc/igc_main.c
>> @@ -641,7 +641,10 @@ static void igc_configure_rx_ring(struct igc_adapter *adapter,
>>   	else
>>   		buf_size = IGC_RXBUFFER_2048;
>>
>> -	srrctl = IGC_RX_HDR_LEN << IGC_SRRCTL_BSIZEHDRSIZE_SHIFT;
>> +	srrctl = rd32(IGC_SRRCTL(reg_idx));
>> +	srrctl &= ~(IGC_SRRCTL_BSIZEPKT_MASK | IGC_SRRCTL_BSIZEHDRSIZE_MASK |
>> +		  IGC_SRRCTL_DESCTYPE_MASK);
>                   ^^
>Please fix indention, moving IGC_SRRCTL_DESCTYPE_MASK such that it aligns
>with IGC_SRRCTL_BSIZEPKT_MASK.  This make is easier for the eye to spot that it
>is part of the negation (~).
Sure. Thanks for your comment. I will fix it in v2.

>
>> +	srrctl |= IGC_RX_HDR_LEN << IGC_SRRCTL_BSIZEHDRSIZE_SHIFT;
>>   	srrctl |= buf_size >> IGC_SRRCTL_BSIZEPKT_SHIFT;
>>   	srrctl |= IGC_SRRCTL_DESCTYPE_ADV_ONEBUF;
>>