nfp: provide a better warning when ring allocation fails

NFP supports fairly enormous ring sizes (up to 256k descriptors).
In commit 46627170 ("nfp: use kvcalloc() to allocate SW buffer
descriptor arrays") we have started using kvcalloc() functions to
make sure the allocation of software state arrays doesn't hit
the MAX_ORDER limit.  Unfortunately, we can't use virtual mappings
for the DMA region holding HW descriptors.  In case this allocation
fails instead of the generic (and fairly scary) warning/splat in
the logs print a helpful message explaining what happened and
suggesting how to fix it.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Dirk van der Merwe <dirk.vandermerwe@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/netronome/nfp/nfp_net_common.c

@@ -2180,9 +2180,13 @@ nfp_net_tx_ring_alloc(struct nfp_net_dp *dp, struct nfp_net_tx_ring *tx_ring)
 
 	tx_ring->size = array_size(tx_ring->cnt, sizeof(*tx_ring->txds));
 	tx_ring->txds = dma_zalloc_coherent(dp->dev, tx_ring->size,
-					    &tx_ring->dma, GFP_KERNEL);
-	if (!tx_ring->txds)
+					    &tx_ring->dma,
+					    GFP_KERNEL | __GFP_NOWARN);
+	if (!tx_ring->txds) {
+		netdev_warn(dp->netdev, "failed to allocate TX descriptor ring memory, requested descriptor count: %d, consider lowering descriptor count\n",
+			    tx_ring->cnt);
 		goto err_alloc;
+	}
 
 	tx_ring->txbufs = kvcalloc(tx_ring->cnt, sizeof(*tx_ring->txbufs),
 				   GFP_KERNEL);
@@ -2334,9 +2338,13 @@ nfp_net_rx_ring_alloc(struct nfp_net_dp *dp, struct nfp_net_rx_ring *rx_ring)
 	rx_ring->cnt = dp->rxd_cnt;
 	rx_ring->size = array_size(rx_ring->cnt, sizeof(*rx_ring->rxds));
 	rx_ring->rxds = dma_zalloc_coherent(dp->dev, rx_ring->size,
-					    &rx_ring->dma, GFP_KERNEL);
-	if (!rx_ring->rxds)
+					    &rx_ring->dma,
+					    GFP_KERNEL | __GFP_NOWARN);
+	if (!rx_ring->rxds) {
+		netdev_warn(dp->netdev, "failed to allocate RX descriptor ring memory, requested descriptor count: %d, consider lowering descriptor count\n",
+			    rx_ring->cnt);
 		goto err_alloc;
+	}
 
 	rx_ring->rxbufs = kvcalloc(rx_ring->cnt, sizeof(*rx_ring->rxbufs),
 				   GFP_KERNEL);