Re: [Intel-wired-lan] [PATCH iwl-next v3] ice: Add E830 checksum offload support

[Alexander Lobakin <aleksander.lobakin@intel.com>]

From: Paul Greenwalt <paul.greenwalt@intel.com>
Date: Tue, 17 Sep 2024 17:45:47 -0400

> E830 supports raw receive and generic transmit checksum offloads.
> 
> Raw receive checksum support is provided by hardware calculating the
> checksum over the whole packet, regardless of type. The calculated
> checksum is provided to driver in the Rx flex descriptor. Then the driver
> assigns the checksum to skb->csum and sets skb->ip_summed to
> CHECKSUM_COMPLETE.
> 
> Generic transmit checksum support is provided by hardware calculating the
> checksum given two offsets: the start offset to begin checksum calculation,
> and the offset to insert the calculated checksum in the packet. Support is
> advertised to the stack using NETIF_F_HW_CSUM feature.
> 
> E830 has the following limitations when both generic transmit checksum
> offload and TCP Segmentation Offload (TSO) are enabled:
> 
> 1. Inner packet header modification is not supported. This restriction
>    includes the inability to alter TCP flags, such as the push flag. As a
>    result, this limitation can impact the receiver's ability to coalesce
>    packets, potentially degrading network throughput.
> 2. The Maximum Segment Size (MSS) is limited to 1023 bytes, which prevents
>    support of Maximum Transmission Unit (MTU) greater than 1063 bytes.
> 
> Therefore NETIF_F_HW_CSUM and NETIF_F_ALL_TSO features are mutually
> exclusive. NETIF_F_HW_CSUM hardware feature support is indicated but is not
> enabled by default. Instead, IP checksums and NETIF_F_ALL_TSO are the
> defaults. Enforcement of mutual exclusivity of NETIF_F_HW_CSUM and
> NETIF_F_ALL_TSO is done in ice_fix_features_tso_gcs(). Mutual exclusivity
> of IP checksums and NETIF_F_HW_CSUM is handled by netdev_fix_features().
> 
> When NETIF_F_HW_CSUM is requested the provided skb->csum_start and
> skb->csum_offset are passed to hardware in the Tx context descriptor
> generic checksum (GCS) parameters. Hardware calculates the 1's complement
> from skb->csum_start to the end of the packet, and inserts the result in
> the packet at skb->csum_offset.
> 
> Co-developed-by: Alice Michael <alice.michael@intel.com>
> Signed-off-by: Alice Michael <alice.michael@intel.com>
> Co-developed-by: Eric Joyner <eric.joyner@intel.com>
> Signed-off-by: Eric Joyner <eric.joyner@intel.com>
> Signed-off-by: Paul Greenwalt <paul.greenwalt@intel.com>

Reviewed-by: Alexander Lobakin <aleksander.lobakin@intel.com>

The only tiny nitpick below. The window opened today, so Tony may ask
you to resubmit the patch so that he could take it.

[...]

> @@ -6283,6 +6321,8 @@ ice_fdb_del(struct ndmsg *ndm, __always_unused struct nlattr *tb[],
>   *	These are mutually exclusive as there is currently no way to
>   *	enable/disable VLAN filtering based on VLAN ethertype when using VLAN
>   *	prune rules.
> + *
> + * Return: updated features list

This change is not related to the series. But I don't have any
objections against it (not sure about the maintainers), so I think you
could leave it here. Just add a period to the end of the sentence.

>   */
>  static netdev_features_t
>  ice_fix_features(struct net_device *netdev, netdev_features_t features)
> @@ -6338,6 +6378,9 @@ ice_fix_features(struct net_device *netdev, netdev_features_t features)
>  		features &= ~NETIF_VLAN_STRIPPING_FEATURES;
>  	}
>  
> +	if (ice_is_feature_supported(np->vsi->back, ICE_F_GCS))
> +		features = ice_fix_features_gcs(netdev, features);
> +
>  	return features;
>  }

Thanks,
Olek