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

[Jesper Dangaard Brouer <jbrouer@redhat.com>]

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 (~).

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