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

["Song, Yoong Siang" <yoong.siang.song@intel.com>]

On Friday, April 14, 2023 2:42 AM, Jesper Dangaard Brouer <jbrouer@redhat.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.
>>
>
>Ah, I believe I have hit this bug with my igc patches.
>Thanks for fixing.
No problem. I found it when testing your patches too.
>
>> 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>
>>
>
>Why port 9092 ?
>The ./xdp_hw_metadata prog will redirect port 9091
Yes, you are right. But this patch is tested without your patches. So, igc Rx
XDP metadata support is not there. We only can test XDP_PASS which
the timestamp is put into skb. xdp_hw_metadata tool will open a SOCK_DGRAM
server on port 9092 to dump out timestamp in skb.

I use xdp_hw_metadata tool to test because it can reproduce the issue well.
This issue happens only when we enable hw timestamp before attach XDP prog.
No issue if enable hw timestamp after attach XDP prog.
>
>
>> Command on Link Partner:
>>    echo -n skb | nc -u -q1 <destination IPv4 addr> 9092
>>
>
>Again port 9092 ?
>
>> Result before this patch:
>>    skb hwtstamp is not found!
>>
>> Result after this patch:
>>    found skb hwtstamp = 1677762212.590696226
>
>I usually use this cmd to see if number is sane:
>
>$ date -d @1677762212
>2023-03-02T14:03:32 CET
>
Since this patch is focusing on hw timestamp enablement. So I
think checking on whether Rx HW timestamp is there when
rx_filter = HWTSTAMP_FILTER_ALL is good enough.

Thanks & Regards
Siang

>
>>
>> Fixes: fc9df2a0b520 ("igc: Enable RX via AF_XDP zero-copy")
>> Cc: <stable@vger.kernel.org> # 5.14+
>> Signed-off-by: Song Yoong Siang <yoong.siang.song@intel.com>
>> ---
>>   drivers/net/ethernet/intel/igc/igc_base.h | 7 +++++--
>>   drivers/net/ethernet/intel/igc/igc_main.c | 5 ++++-
>>   2 files changed, 9 insertions(+), 3 deletions(-)
>>
>> 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);
>> +	srrctl |= IGC_RX_HDR_LEN << IGC_SRRCTL_BSIZEHDRSIZE_SHIFT;
>>   	srrctl |= buf_size >> IGC_SRRCTL_BSIZEPKT_SHIFT;
>>   	srrctl |= IGC_SRRCTL_DESCTYPE_ADV_ONEBUF;
>>