eth: fbnic: Configure RDE settings for pause frame

fbnic supports pause frames. When pause frames are enabled presumably
user expects lossless operation from the NIC. Make sure we configure
RDE (Rx DMA Engine) to DROP_NEVER mode to avoid discards due to delays
in fetching Rx descriptors from the host.

While at it enable DROP_NEVER when NIC only has a single queue
configured. In this case the NIC acts as a FIFO so there's no risk
of head-of-line blocking other queues by making RDE wait. If pause
is disabled this just moves the packet loss from the DMA engine to
the Rx buffer.

Remove redundant call to fbnic_config_drop_mode_rcq(), introduced by
commit 0cb4c0a13723 ("eth: fbnic: Implement Rx queue
alloc/start/stop/free"). This call does not add value as
fbnic_enable_rcq(), which is called immediately afterward, already
handles this.

Although we do not support autoneg at this time, preserve tx_pause in
.mac_link_up instead of fbnic_phylink_get_pauseparam()

Signed-off-by: Mohsin Bashir <[e-mail]>
Reviewed-by: Andrew Lunn <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/ethernet/meta/fbnic/fbnic_netdev.h

···
 
 	/* Time stamping filter config */
 	struct kernel_hwtstamp_config hwtstamp_config;
+
+	bool tx_pause;
 };
 
 int __fbnic_open(struct fbnic_net *fbn);

drivers/net/ethernet/meta/fbnic/fbnic_phylink.c

···
 	struct fbnic_net *fbn = netdev_priv(netdev);
 	struct fbnic_dev *fbd = fbn->fbd;
 
+	fbn->tx_pause = tx_pause;
+	fbnic_config_drop_mode(fbn, tx_pause);
+
 	fbd->mac->link_up(fbd, tx_pause, rx_pause);
 }
 

drivers/net/ethernet/meta/fbnic/fbnic_txrx.c

···
 }
 
 static void fbnic_config_drop_mode_rcq(struct fbnic_napi_vector *nv,
-				       struct fbnic_ring *rcq)
+				       struct fbnic_ring *rcq, bool tx_pause)
 {
+	struct fbnic_net *fbn = netdev_priv(nv->napi.dev);
 	u32 drop_mode, rcq_ctl;
 
-	drop_mode = FBNIC_QUEUE_RDE_CTL0_DROP_IMMEDIATE;
+	if (!tx_pause && fbn->num_rx_queues > 1)
+		drop_mode = FBNIC_QUEUE_RDE_CTL0_DROP_IMMEDIATE;
+	else
+		drop_mode = FBNIC_QUEUE_RDE_CTL0_DROP_NEVER;
 
 	/* Specify packet layout */
 	rcq_ctl = FIELD_PREP(FBNIC_QUEUE_RDE_CTL0_DROP_MODE_MASK, drop_mode) |
···
 	    FIELD_PREP(FBNIC_QUEUE_RDE_CTL0_MIN_TROOM_MASK, FBNIC_RX_TROOM);
 
 	fbnic_ring_wr32(rcq, FBNIC_QUEUE_RDE_CTL0, rcq_ctl);
+}
+
+void fbnic_config_drop_mode(struct fbnic_net *fbn, bool tx_pause)
+{
+	int i, t;
+
+	for (i = 0; i < fbn->num_napi; i++) {
+		struct fbnic_napi_vector *nv = fbn->napi[i];
+
+		for (t = 0; t < nv->rxt_count; t++) {
+			struct fbnic_q_triad *qt = &nv->qt[nv->txt_count + t];
+
+			fbnic_config_drop_mode_rcq(nv, &qt->cmpl, tx_pause);
+		}
+	}
 }
 
 static void fbnic_config_rim_threshold(struct fbnic_ring *rcq, u16 nv_idx, u32 rx_desc)
···
 	u32 hds_thresh = fbn->hds_thresh;
 	u32 rcq_ctl = 0;
 
-	fbnic_config_drop_mode_rcq(nv, rcq);
+	fbnic_config_drop_mode_rcq(nv, rcq, fbn->tx_pause);
 
 	/* Force lower bound on MAX_HEADER_BYTES. Below this, all frames should
 	 * be split at L4. It would also result in the frames being split at
···
 						  &nv->napi);
 
 		fbnic_enable_bdq(&qt->sub0, &qt->sub1);
-		fbnic_config_drop_mode_rcq(nv, &qt->cmpl);
 		fbnic_enable_rcq(nv, &qt->cmpl);
 	}
 }

drivers/net/ethernet/meta/fbnic/fbnic_txrx.h

···
 irqreturn_t fbnic_msix_clean_rings(int irq, void *data);
 void fbnic_napi_enable(struct fbnic_net *fbn);
 void fbnic_napi_disable(struct fbnic_net *fbn);
+void fbnic_config_drop_mode(struct fbnic_net *fbn, bool tx_pause);
 void fbnic_enable(struct fbnic_net *fbn);
 void fbnic_disable(struct fbnic_net *fbn);
 void fbnic_flush(struct fbnic_net *fbn);