[PATCH net] net: ti: icssg-prueth: Fix skb handling for XDP_PASS

[Jakub Kicinski]

On Mon, 21 Jul 2025 18:19:18 +0530 Meghana Malladi wrote:
> diff --git a/drivers/net/ethernet/ti/icssg/icssg_common.c b/drivers/net/ethernet/ti/icssg/icssg_common.c
> index 12f25cec6255..a0e7def33e8e 100644
> --- a/drivers/net/ethernet/ti/icssg/icssg_common.c
> +++ b/drivers/net/ethernet/ti/icssg/icssg_common.c
> @@ -757,15 +757,12 @@ static int emac_rx_packet(struct prueth_emac *emac, u32 flow_id, u32 *xdp_state)
>  		xdp_prepare_buff(&xdp, pa, PRUETH_HEADROOM, pkt_len, false);
>  
>  		*xdp_state = emac_run_xdp(emac, &xdp, page, &pkt_len);
> -		if (*xdp_state == ICSSG_XDP_PASS)
> -			skb = xdp_build_skb_from_buff(&xdp);
> -		else
> +		if (*xdp_state != ICSSG_XDP_PASS)
>  			goto requeue;
> -	} else {
> -		/* prepare skb and send to n/w stack */
> -		skb = napi_build_skb(pa, PAGE_SIZE);
>  	}
>  
> +	/* prepare skb and send to n/w stack */
> +	skb = napi_build_skb(pa, PAGE_SIZE);
>  	if (!skb) {
>  		ndev->stats.rx_dropped++;
>  		page_pool_recycle_direct(pool, page);

I'm not sure this is correct. We seem to hardcode headroom to
PRUETH_HEADROOM lower in this function. If XDP adds or removes
network headers and then returns XDP_PASS we'll look for the packet 
at the wrong offset.

We just merged some XDP tests, could you try running 
tools/testing/selftests/drivers/net/xdp.py ? 
Some general instructions can be found here:
https://github.com/linux-netdev/nipa/wiki/Running-driver-tests

Not sure how stable the test is for all NICs but I think the 
 xdp.test_xdp_native_adjst_head_grow_data
test case will exercise what I'm suspecting will fail.