Re: [PATCH v6 RESEND net-next 1/5] net: enetc: add Rx checksum offload for i.MX95 ENETC

[Simon Horman]

On Wed, Dec 04, 2024 at 01:29:28PM +0800, Wei Fang wrote:
> ENETC rev 4.1 supports TCP and UDP checksum offload for receive, the bit
> 108 of the Rx BD will be set if the TCP/UDP checksum is correct. Since
> this capability is not defined in register, the rx_csum bit is added to
> struct enetc_drvdata to indicate whether the device supports Rx checksum
> offload.
> 
> Signed-off-by: Wei Fang <wei.fang@xxxxxxx>
> Reviewed-by: Frank Li <Frank.Li@xxxxxxx>
> Reviewed-by: Claudiu Manoil <claudiu.manoil@xxxxxxx>
> ---
> v2: no changes
> v3: no changes
> v4: no changes
> v5: no changes
> v6: no changes
> ---
>  drivers/net/ethernet/freescale/enetc/enetc.c       | 14 ++++++++++----
>  drivers/net/ethernet/freescale/enetc/enetc.h       |  2 ++
>  drivers/net/ethernet/freescale/enetc/enetc_hw.h    |  2 ++
>  .../net/ethernet/freescale/enetc/enetc_pf_common.c |  3 +++
>  4 files changed, 17 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/ethernet/freescale/enetc/enetc.c b/drivers/net/ethernet/freescale/enetc/enetc.c
> index 35634c516e26..3137b6ee62d3 100644
> --- a/drivers/net/ethernet/freescale/enetc/enetc.c
> +++ b/drivers/net/ethernet/freescale/enetc/enetc.c
> @@ -1011,10 +1011,15 @@ static void enetc_get_offloads(struct enetc_bdr *rx_ring,
>  
>  	/* TODO: hashing */
>  	if (rx_ring->ndev->features & NETIF_F_RXCSUM) {
> -		u16 inet_csum = le16_to_cpu(rxbd->r.inet_csum);
> -
> -		skb->csum = csum_unfold((__force __sum16)~htons(inet_csum));
> -		skb->ip_summed = CHECKSUM_COMPLETE;
> +		if (priv->active_offloads & ENETC_F_RXCSUM &&
> +		    le16_to_cpu(rxbd->r.flags) & ENETC_RXBD_FLAG_L4_CSUM_OK) {
> +			skb->ip_summed = CHECKSUM_UNNECESSARY;
> +		} else {
> +			u16 inet_csum = le16_to_cpu(rxbd->r.inet_csum);
> +
> +			skb->csum = csum_unfold((__force __sum16)~htons(inet_csum));
> +			skb->ip_summed = CHECKSUM_COMPLETE;
> +		}
>  	}

Hi Wei,

I am wondering about the relationship between the above and
hardware support for CHECKSUM_COMPLETE.

Prior to this patch CHECKSUM_COMPLETE was always used, which seems
desirable. But with this patch, CHECKSUM_UNNECESSARY is conditionally used.

If those cases don't work with CHECKSUM_COMPLETE then is this a bug-fix?

Or, alternatively, if those cases do work with CHECKSUM_COMPLETE, then
I'm unsure why this change is necessary or desirable. It's my understanding
that from the Kernel's perspective CHECKSUM_COMPLETE is preferable to
CHECKSUM_UNNECESSARY.

...