[PATCH v2 net 3/8] ice: do not round up result of dbuf calculation for xsk pool

[Maciej Fijalkowski <maciej.fijalkowski@intel.com>]

When programming dbuf on rx queue context, avoid division round up as
it causes to actually corrupt the tailroom for AF_XDP ZC. Below is an
example based on 4k chunk size when xsk pool pointer is valid on given
rx ring:

chunk_size = 4096
headroom = 256
tailroom = 320

ring->rx_buf_len = 4096 - 256 - 320 = 3520

rx_ctx.dbuf = DIV_ROUND_UP(3520, 128) ->
3520 / 128 = 27.5 -> round up results in 28

dbuf programming unit is 128. If we give 128 * 28 = 3584. So HW will
corrupt 64 bytes from tailroom. Decrement dbuf by 1 when xsk_pool is
present on given ice_rx_ring.

Also, restore ::rx_buf_len setting via xsk_pool_get_rx_frame_size() as
of now it respects the tailroom.

Fixes: 1bbc04de607b ("ice: xsk: add RX multi-buffer support")
Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
---
 drivers/net/ethernet/intel/ice/ice_base.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/net/ethernet/intel/ice/ice_base.c b/drivers/net/ethernet/intel/ice/ice_base.c
index 1667f686ff75..f9514d7bb83c 100644
--- a/drivers/net/ethernet/intel/ice/ice_base.c
+++ b/drivers/net/ethernet/intel/ice/ice_base.c
@@ -500,6 +500,8 @@ static int ice_setup_rx_ctx(struct ice_rx_ring *ring)
 	 */
 	rlan_ctx.dbuf = DIV_ROUND_UP(ring->rx_buf_len,
 				     BIT_ULL(ICE_RLAN_CTX_DBUF_S));
+	if (ring->xsk_pool)
+		rlan_ctx.dbuf--;
 
 	/* use 32 byte descriptors */
 	rlan_ctx.dsize = 1;
@@ -673,6 +675,9 @@ static int ice_vsi_cfg_rxq(struct ice_rx_ring *ring)
 		if (ring->xsk_pool) {
 			u32 frag_size =
 				xsk_pool_get_rx_frag_step(ring->xsk_pool);
+
+			ring->rx_buf_len =
+				xsk_pool_get_rx_frame_size(ring->xsk_pool);
 			err = __xdp_rxq_info_reg(&ring->xdp_rxq, ring->netdev,
 						 ring->q_index,
 						 ring->q_vector->napi.napi_id,
-- 
2.43.0