[Intel-wired-lan] [PATCH intel-net 3/5] ice: xsk: do not clear status_error0 for ntu + nb_buffs descriptor

[Alexander Lobakin]

From: Maciej Fijalkowski <maciej.fijalkowski at intel.com>
Date: Fri, 10 Dec 2021 15:59:39 +0100

> The descriptor that ntu is pointing at when we exit
> ice_alloc_rx_bufs_zc() should not have its corresponding DD bit cleared
> as descriptor is not allocated in there and it is not valid for HW
> usage.
> 
> The allocation routine at the entry will fill the descriptor that ntu
> points to after it was set to ntu + nb_buffs on previous call.
> 
> Even the spec says:
> "The tail pointer should be set to one descriptor beyond the last empty
> descriptor in host descriptor ring."
> 
> Therefore, step away from clearing the status_error0 on ntu + nb_buffs
> descriptor.
> 
> Fixes: db804cfc21e9 ("ice: Use the xsk batched rx allocation interface")
> Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski at intel.com>
> ---
>  drivers/net/ethernet/intel/ice/ice_xsk.c | 7 +------
>  1 file changed, 1 insertion(+), 6 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/ice/ice_xsk.c b/drivers/net/ethernet/intel/ice/ice_xsk.c
> index 5cb61955c1f3..874fce9fa1c3 100644
> --- a/drivers/net/ethernet/intel/ice/ice_xsk.c
> +++ b/drivers/net/ethernet/intel/ice/ice_xsk.c
> @@ -394,14 +394,9 @@ bool ice_alloc_rx_bufs_zc(struct ice_rx_ring *rx_ring, u16 count)
>  	}
>  
>  	ntu += nb_buffs;
> -	if (ntu == rx_ring->count) {
> -		rx_desc = ICE_RX_DESC(rx_ring, 0);
> -		xdp = rx_ring->xdp_buf;
> +	if (ntu == rx_ring->count)

Maybe use unlikely() here while at it? 1/512 (depending on ring
size) chance is low enough.

>  		ntu = 0;
> -	}
>  
> -	/* clear the status bits for the next_to_use descriptor */
> -	rx_desc->wb.status_error0 = 0;
>  	ice_release_rx_desc(rx_ring, ntu);

This interferes with my patch in next-queue ([0]) (well, supersedes
it to be precise).
Tony, what would be better to do with it, just drop mine or correct
this one (it would become an oneliner removing status_error0
assignment then)?

>  
>  	return count == nb_buffs;
> -- 
> 2.33.1

[0] https://lore.kernel.org/netdev/20211130183649.1166842-2-alexandr.lobakin@intel.com

Al