sfc: Enable RX DMA scattering where possible

Enable RX DMA scattering iff an RX buffer large enough for the current
MTU will not fit into a single page and the NIC supports DMA
scattering for kernel-mode RX queues.

On Falcon and Siena, the RX_USR_BUF_SIZE field is used as the DMA
limit for both all RX queues with scatter enabled.  Set it to 1824,
matching what Onload uses now.

Maintain a statistic for frames truncated due to lack of descriptors
(rx_nodesc_trunc).  This is distinct from rx_frm_trunc which may be
incremented when scattering is disabled and implies an over-length
frame.

Whenever an MTU change causes scattering to be turned on or off,
update filters that point to the PF queues, but leave others
unchanged, as VF drivers assume scattering is off.

Add n_frags parameters to various functions, and make them iterate:
- efx_rx_packet()
- efx_recycle_rx_buffers()
- efx_rx_mk_skb()
- efx_rx_deliver()

Make efx_handle_rx_event() responsible for updating
efx_rx_queue::removed_count.

Change the RX pipeline state to a starting ring index and number of
fragments, and make __efx_rx_packet() responsible for clearing it.

Based on earlier versions by David Riddoch and Jon Cooper.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>

1 files changed, 29 insertions, 5 deletions

diff --git a/drivers/net/ethernet/sfc/efx.c b/drivers/net/ethernet/sfc/efx.c
index f8013c3ea37..1213af5024d 100644
--- a/drivers/net/ethernet/sfc/efx.c
+++ b/drivers/net/ethernet/sfc/efx.c
@@ -88,8 +88,6 @@ const char *const efx_reset_type_names[] = {
 	[RESET_TYPE_MC_FAILURE]         = "MC_FAILURE",
 };
 
-#define EFX_MAX_MTU (9 * 1024)
-
 /* Reset workqueue. If any NIC has a hardware failure then a reset will be
  * queued onto this work queue. This is not a per-nic work queue, because
  * efx_reset_work() acquires the rtnl lock, so resets are naturally serialised.
@@ -627,9 +625,11 @@ fail:
  */
 static void efx_start_datapath(struct efx_nic *efx)
 {
+	bool old_rx_scatter = efx->rx_scatter;
 	struct efx_tx_queue *tx_queue;
 	struct efx_rx_queue *rx_queue;
 	struct efx_channel *channel;
+	size_t rx_buf_len;
 
 	/* Calculate the rx buffer allocation parameters required to
 	 * support the current MTU, including padding for header
@@ -638,8 +638,32 @@ static void efx_start_datapath(struct efx_nic *efx)
 	efx->rx_dma_len = (efx->type->rx_buffer_hash_size +
 			   EFX_MAX_FRAME_LEN(efx->net_dev->mtu) +
 			   efx->type->rx_buffer_padding);
-	efx->rx_buffer_order = get_order(sizeof(struct efx_rx_page_state) +
-					 EFX_PAGE_IP_ALIGN + efx->rx_dma_len);
+	rx_buf_len = (sizeof(struct efx_rx_page_state) +
+		      EFX_PAGE_IP_ALIGN + efx->rx_dma_len);
+	if (rx_buf_len <= PAGE_SIZE) {
+		efx->rx_scatter = false;
+		efx->rx_buffer_order = 0;
+		if (rx_buf_len <= PAGE_SIZE / 2)
+			efx->rx_buffer_truesize = PAGE_SIZE / 2;
+		else
+			efx->rx_buffer_truesize = PAGE_SIZE;
+	} else if (efx->type->can_rx_scatter) {
+		BUILD_BUG_ON(sizeof(struct efx_rx_page_state) +
+			     EFX_PAGE_IP_ALIGN + EFX_RX_USR_BUF_SIZE >
+			     PAGE_SIZE / 2);
+		efx->rx_scatter = true;
+		efx->rx_dma_len = EFX_RX_USR_BUF_SIZE;
+		efx->rx_buffer_order = 0;
+		efx->rx_buffer_truesize = PAGE_SIZE / 2;
+	} else {
+		efx->rx_scatter = false;
+		efx->rx_buffer_order = get_order(rx_buf_len);
+		efx->rx_buffer_truesize = PAGE_SIZE << efx->rx_buffer_order;
+	}
+
+	/* RX filters also have scatter-enabled flags */
+	if (efx->rx_scatter != old_rx_scatter)
+		efx_filter_update_rx_scatter(efx);
 
 	/* We must keep at least one descriptor in a TX ring empty.
 	 * We could avoid this when the queue size does not exactly
@@ -661,7 +685,7 @@ static void efx_start_datapath(struct efx_nic *efx)
 			efx_nic_generate_fill_event(rx_queue);
 		}
 
-		WARN_ON(channel->rx_pkt != NULL);
+		WARN_ON(channel->rx_pkt_n_frags);
 	}
 
 	if (netif_device_present(efx->net_dev))