net: bcmgenet: collect Rx discarded packet count

Bits 31:16 of RDMA_PROD_INDEX contain Rx discarded packet count, which
are the Rx packets that had to be dropped by MAC hardware since there
was no room on the Rx queue. Add code to collect this information into
the netdev stats.

Signed-off-by: Petri Gynther <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/ethernet/broadcom/genet/bcmgenet.c

···
 	int len, err;
 	unsigned int rxpktprocessed = 0, rxpkttoprocess;
 	unsigned int p_index;
+	unsigned int discards;
 	unsigned int chksum_ok = 0;
 
 	p_index = bcmgenet_rdma_ring_readl(priv, index, RDMA_PROD_INDEX);
+
+	discards = (p_index >> DMA_P_INDEX_DISCARD_CNT_SHIFT) &
+		   DMA_P_INDEX_DISCARD_CNT_MASK;
+	if (discards > ring->old_discards) {
+		discards = discards - ring->old_discards;
+		dev->stats.rx_missed_errors += discards;
+		dev->stats.rx_errors += discards;
+		ring->old_discards += discards;
+
+		/* Clear HW register when we reach 75% of maximum 0xFFFF */
+		if (ring->old_discards >= 0xC000) {
+			ring->old_discards = 0;
+			bcmgenet_rdma_ring_writel(priv, index, 0,
+						  RDMA_PROD_INDEX);
+		}
+	}
+
 	p_index &= DMA_P_INDEX_MASK;
 
 	if (likely(p_index >= ring->c_index))

drivers/net/ethernet/broadcom/genet/bcmgenet.h

···
 	unsigned int	read_ptr;	/* Rx ring read pointer */
 	unsigned int	cb_ptr;		/* Rx ring initial CB ptr */
 	unsigned int	end_ptr;	/* Rx ring end CB ptr */
+	unsigned int	old_discards;
 };
 
 /* device context */