Merge branch 'sfc-tx-queues'

Íñigo Huguet says:

====================
sfc: Fix lack of XDP TX queues

A change introduced in commit e26ca4b5 ("sfc: reduce the number of
requested xdp ev queues") created a bug in XDP_TX and XDP_REDIRECT
because it unintentionally reduced the number of XDP TX queues, letting
not enough queues to have one per CPU, which leaded to errors if XDP
TX/REDIRECT was done from a high numbered CPU.

This patchs make the following changes:
- Fix the bug mentioned above
- Revert commit 99ba0ea6 ("sfc: adjust efx->xdp_tx_queue_count with
  the real number of initialized queues") which intended to fix a related
  problem, created by mentioned bug, but it's no longer necessary
- Add a new error log message if there are not enough resources to make
  XDP_TX/REDIRECT work

V1 -> V2: keep the calculation of how many tx queues can handle a single
event queue, but apply the "max. tx queues per channel" upper limit.
V2 -> V3: WARN_ON if the number of initialized XDP TXQs differs from the
expected.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/sfc/efx_channels.c

@@ -152,6 +152,7 @@ static int efx_allocate_msix_channels(struct efx_nic *efx,
 	 * maximum size.
 	 */
 	tx_per_ev = EFX_MAX_EVQ_SIZE / EFX_TXQ_MAX_ENT(efx);
+	tx_per_ev = min(tx_per_ev, EFX_MAX_TXQ_PER_CHANNEL);
 	n_xdp_tx = num_possible_cpus();
 	n_xdp_ev = DIV_ROUND_UP(n_xdp_tx, tx_per_ev);
 
@@ -169,6 +170,8 @@ static int efx_allocate_msix_channels(struct efx_nic *efx,
 		netif_err(efx, drv, efx->net_dev,
 			  "Insufficient resources for %d XDP event queues (%d other channels, max %d)\n",
 			  n_xdp_ev, n_channels, max_channels);
+		netif_err(efx, drv, efx->net_dev,
+			  "XDP_TX and XDP_REDIRECT will not work on this interface");
 		efx->n_xdp_channels = 0;
 		efx->xdp_tx_per_channel = 0;
 		efx->xdp_tx_queue_count = 0;
@@ -176,12 +179,14 @@ static int efx_allocate_msix_channels(struct efx_nic *efx,
 		netif_err(efx, drv, efx->net_dev,
 			  "Insufficient resources for %d XDP TX queues (%d other channels, max VIs %d)\n",
 			  n_xdp_tx, n_channels, efx->max_vis);
+		netif_err(efx, drv, efx->net_dev,
+			  "XDP_TX and XDP_REDIRECT will not work on this interface");
 		efx->n_xdp_channels = 0;
 		efx->xdp_tx_per_channel = 0;
 		efx->xdp_tx_queue_count = 0;
 	} else {
 		efx->n_xdp_channels = n_xdp_ev;
-		efx->xdp_tx_per_channel = EFX_MAX_TXQ_PER_CHANNEL;
+		efx->xdp_tx_per_channel = tx_per_ev;
 		efx->xdp_tx_queue_count = n_xdp_tx;
 		n_channels += n_xdp_ev;
 		netif_dbg(efx, drv, efx->net_dev,
@@ -891,18 +896,20 @@ int efx_set_channels(struct efx_nic *efx)
 			if (efx_channel_is_xdp_tx(channel)) {
 				efx_for_each_channel_tx_queue(tx_queue, channel) {
 					tx_queue->queue = next_queue++;
-					netif_dbg(efx, drv, efx->net_dev, "Channel %u TXQ %u is XDP %u, HW %u\n",
-						  channel->channel, tx_queue->label,
-						  xdp_queue_number, tx_queue->queue);
+
 					/* We may have a few left-over XDP TX
 					 * queues owing to xdp_tx_queue_count
 					 * not dividing evenly by EFX_MAX_TXQ_PER_CHANNEL.
 					 * We still allocate and probe those
 					 * TXQs, but never use them.
 					 */
-					if (xdp_queue_number < efx->xdp_tx_queue_count)
+					if (xdp_queue_number < efx->xdp_tx_queue_count) {
+						netif_dbg(efx, drv, efx->net_dev, "Channel %u TXQ %u is XDP %u, HW %u\n",
+							  channel->channel, tx_queue->label,
+							  xdp_queue_number, tx_queue->queue);
 						efx->xdp_tx_queues[xdp_queue_number] = tx_queue;
-					xdp_queue_number++;
+						xdp_queue_number++;
+					}
 				}
 			} else {
 				efx_for_each_channel_tx_queue(tx_queue, channel) {
@@ -914,8 +921,7 @@ int efx_set_channels(struct efx_nic *efx)
 			}
 		}
 	}
-	if (xdp_queue_number)
-		efx->xdp_tx_queue_count = xdp_queue_number;
+	WARN_ON(xdp_queue_number != efx->xdp_tx_queue_count);
 
 	rc = netif_set_real_num_tx_queues(efx->net_dev, efx->n_tx_channels);
 	if (rc)