Re: [PATCH net v5 1/2] net: ethernet: cortina: Drop software checksum and TSO

[Vladimir Oltean <olteanv@gmail.com>]

On Tue, Jan 02, 2024 at 09:34:25PM +0100, Linus Walleij wrote:
> @@ -1143,39 +1142,13 @@ static int gmac_map_tx_bufs(struct net_device *netdev, struct sk_buff *skb,
>  	struct gmac_txdesc *txd;
>  	skb_frag_t *skb_frag;
>  	dma_addr_t mapping;
> -	unsigned short mtu;
>  	void *buffer;
> -	int ret;
> -
> -	mtu  = ETH_HLEN;
> -	mtu += netdev->mtu;
> -	if (skb->protocol == htons(ETH_P_8021Q))
> -		mtu += VLAN_HLEN;
>  
> +	/* TODO: implement proper TSO using MTU in word3 */
>  	word1 = skb->len;
> -	word3 = SOF_BIT;
> -
> -	if (word1 > mtu) {
> -		word1 |= TSS_MTU_ENABLE_BIT;
> -		word3 |= mtu;
> -	}
> +	word3 = SOF_BIT | skb->len;
>  
> -	if (skb->len >= ETH_FRAME_LEN) {
> -		/* Hardware offloaded checksumming isn't working on frames
> -		 * bigger than 1514 bytes. A hypothesis about this is that the
> -		 * checksum buffer is only 1518 bytes, so when the frames get
> -		 * bigger they get truncated, or the last few bytes get
> -		 * overwritten by the FCS.
> -		 *
> -		 * Just use software checksumming and bypass on bigger frames.
> -		 */
> -		if (skb->ip_summed == CHECKSUM_PARTIAL) {
> -			ret = skb_checksum_help(skb);
> -			if (ret)
> -				return ret;
> -		}
> -		word1 |= TSS_BYPASS_BIT;
> -	} else if (skb->ip_summed == CHECKSUM_PARTIAL) {

So are you taking back the statement that "Hardware offloaded
checksumming isn't working on frames bigger than 1514 bytes"?

Have you increased the interface MTU beyond 1500, and tested with plain
TCP (no DSA) on top of it? Who will provide the TCP checksum for them now?

I don't understand why you remove the skb_checksum_help() call.
It doesn't play nice with skb_is_gso() packets, agreed, but you removed
the TSO netdev feature.

> +	if (skb->ip_summed == CHECKSUM_PARTIAL) {
>  		int tcp = 0;
>  
>  		/* We do not switch off the checksumming on non TCP/UDP
> 
> -- 
> 2.34.1
>