Re: [PATCH net 4/4] net: ethernet: cortina: Handle large frames

[Andrew Lunn <andrew@lunn.ch>]

> @@ -1170,7 +1171,14 @@ static int gmac_map_tx_bufs(struct net_device *netdev, struct sk_buff *skb,
>  		word3 |= mtu;
>  	}
>  
> -	if (skb->ip_summed != CHECKSUM_NONE) {
> +	if (skb->len >= ETH_FRAME_LEN) {
> +		/* Hardware offloaded checksumming isn't working on frames
> +		 * bigger than 1514 bytes. Perhaps the buffer is only 1518
> +		 * bytes fitting mach a normal frame and a checksum?

mach ?

> +		 * Just bypass on bigger frames.
> +		 */
> +		word1 |= TSS_BYPASS_BIT;
> +	} else if (skb->ip_summed != CHECKSUM_NONE) {

I've never looked at how the network stack does checksums. But looking
at this patch, it made me wounder, how do you tell the stack it needs
to do a software checksum because the hardware cannot? Or for this
driver, is it always calculating a checksum, which is then ignored?
Maybe you can improve performance a little but disabling software
checksum when it is not needed?

	 Andrew