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, 71 insertions, 3 deletions

diff --git a/drivers/net/ethernet/sfc/filter.c b/drivers/net/ethernet/sfc/filter.c
index 61b4408bbdb..2397f0e8d3e 100644
--- a/drivers/net/ethernet/sfc/filter.c
+++ b/drivers/net/ethernet/sfc/filter.c
@@ -172,6 +172,25 @@ static void efx_filter_push_rx_config(struct efx_nic *efx)
 			filter_ctl, FRF_CZ_MULTICAST_NOMATCH_RSS_ENABLED,
 			!!(table->spec[EFX_FILTER_INDEX_MC_DEF].flags &
 			   EFX_FILTER_FLAG_RX_RSS));
+
+		/* There is a single bit to enable RX scatter for all
+		 * unmatched packets.  Only set it if scatter is
+		 * enabled in both filter specs.
+		 */
+		EFX_SET_OWORD_FIELD(
+			filter_ctl, FRF_BZ_SCATTER_ENBL_NO_MATCH_Q,
+			!!(table->spec[EFX_FILTER_INDEX_UC_DEF].flags &
+			   table->spec[EFX_FILTER_INDEX_MC_DEF].flags &
+			   EFX_FILTER_FLAG_RX_SCATTER));
+	} else if (efx_nic_rev(efx) >= EFX_REV_FALCON_B0) {
+		/* We don't expose 'default' filters because unmatched
+		 * packets always go to the queue number found in the
+		 * RSS table.  But we still need to set the RX scatter
+		 * bit here.
+		 */
+		EFX_SET_OWORD_FIELD(
+			filter_ctl, FRF_BZ_SCATTER_ENBL_NO_MATCH_Q,
+			efx->rx_scatter);
 	}
 
 	efx_writeo(efx, &filter_ctl, FR_BZ_RX_FILTER_CTL);
@@ -413,13 +432,18 @@ static void efx_filter_reset_rx_def(struct efx_nic *efx, unsigned filter_idx)
 	struct efx_filter_state *state = efx->filter_state;
 	struct efx_filter_table *table = &state->table[EFX_FILTER_TABLE_RX_DEF];
 	struct efx_filter_spec *spec = &table->spec[filter_idx];
+	enum efx_filter_flags flags = 0;
 
 	/* If there's only one channel then disable RSS for non VF
 	 * traffic, thereby allowing VFs to use RSS when the PF can't.
 	 */
-	efx_filter_init_rx(spec, EFX_FILTER_PRI_MANUAL,
-			   efx->n_rx_channels > 1 ? EFX_FILTER_FLAG_RX_RSS : 0,
-			   0);
+	if (efx->n_rx_channels > 1)
+		flags |= EFX_FILTER_FLAG_RX_RSS;
+
+	if (efx->rx_scatter)
+		flags |= EFX_FILTER_FLAG_RX_SCATTER;
+
+	efx_filter_init_rx(spec, EFX_FILTER_PRI_MANUAL, flags, 0);
 	spec->type = EFX_FILTER_UC_DEF + filter_idx;
 	table->used_bitmap[0] |= 1 << filter_idx;
 }
@@ -1101,6 +1125,50 @@ void efx_remove_filters(struct efx_nic *efx)
 	kfree(state);
 }
 
+/* Update scatter enable flags for filters pointing to our own RX queues */
+void efx_filter_update_rx_scatter(struct efx_nic *efx)
+{
+	struct efx_filter_state *state = efx->filter_state;
+	enum efx_filter_table_id table_id;
+	struct efx_filter_table *table;
+	efx_oword_t filter;
+	unsigned int filter_idx;
+
+	spin_lock_bh(&state->lock);
+
+	for (table_id = EFX_FILTER_TABLE_RX_IP;
+	     table_id <= EFX_FILTER_TABLE_RX_DEF;
+	     table_id++) {
+		table = &state->table[table_id];
+
+		for (filter_idx = 0; filter_idx < table->size; filter_idx++) {
+			if (!test_bit(filter_idx, table->used_bitmap) ||
+			    table->spec[filter_idx].dmaq_id >=
+			    efx->n_rx_channels)
+				continue;
+
+			if (efx->rx_scatter)
+				table->spec[filter_idx].flags |=
+					EFX_FILTER_FLAG_RX_SCATTER;
+			else
+				table->spec[filter_idx].flags &=
+					~EFX_FILTER_FLAG_RX_SCATTER;
+
+			if (table_id == EFX_FILTER_TABLE_RX_DEF)
+				/* Pushed by efx_filter_push_rx_config() */
+				continue;
+
+			efx_filter_build(&filter, &table->spec[filter_idx]);
+			efx_writeo(efx, &filter,
+				   table->offset + table->step * filter_idx);
+		}
+	}
+
+	efx_filter_push_rx_config(efx);
+
+	spin_unlock_bh(&state->lock);
+}
+
 #ifdef CONFIG_RFS_ACCEL
 
 int efx_filter_rfs(struct net_device *net_dev, const struct sk_buff *skb,