net: mvneta: Convert to be 64 bits compatible

Prepare the mvneta driver in order to be usable on the 64 bits platform
such as the Armada 3700.

[gregory.clement@free-electrons.com]: this patch was extract from a larger
one to ease review and maintenance.
Signed-off-by: Marcin Wojtas <mw@semihalf.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Tested-by: Marcin Wojtas <mw@semihalf.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/marvell/mvneta.c

@@ -296,6 +296,12 @@
 /* descriptor aligned size */
 #define MVNETA_DESC_ALIGNED_SIZE	32
 
+/* Number of bytes to be taken into account by HW when putting incoming data
+ * to the buffers. It is needed in case NET_SKB_PAD exceeds maximum packet
+ * offset supported in MVNETA_RXQ_CONFIG_REG(q) registers.
+ */
+#define MVNETA_RX_PKT_OFFSET_CORRECTION		64
+
 #define MVNETA_RX_PKT_SIZE(mtu) \
 	ALIGN((mtu) + MVNETA_MH_SIZE + MVNETA_VLAN_TAG_LEN + \
 	      ETH_HLEN + ETH_FCS_LEN,			     \
@@ -416,6 +422,7 @@ struct mvneta_port {
 	u64 ethtool_stats[ARRAY_SIZE(mvneta_statistics)];
 
 	u32 indir[MVNETA_RSS_LU_TABLE_SIZE];
+	u16 rx_offset_correction;
 };
 
 /* The mvneta_tx_desc and mvneta_rx_desc structures describe the
@@ -1807,6 +1814,7 @@ static int mvneta_rx_refill(struct mvneta_port *pp,
 		return -ENOMEM;
 	}
 
+	phys_addr += pp->rx_offset_correction;
 	mvneta_rx_desc_fill(rx_desc, phys_addr, data, rxq);
 	return 0;
 }
@@ -2782,7 +2790,7 @@ static int mvneta_rxq_init(struct mvneta_port *pp,
 	mvreg_write(pp, MVNETA_RXQ_SIZE_REG(rxq->id), rxq->size);
 
 	/* Set Offset */
-	mvneta_rxq_offset_set(pp, rxq, NET_SKB_PAD);
+	mvneta_rxq_offset_set(pp, rxq, NET_SKB_PAD - pp->rx_offset_correction);
 
 	/* Set coalescing pkts and time */
 	mvneta_rx_pkts_coal_set(pp, rxq, rxq->pkts_coal);
@@ -4033,6 +4041,13 @@ static int mvneta_probe(struct platform_device *pdev)
 
 	pp->rxq_def = rxq_def;
 
+	/* Set RX packet offset correction for platforms, whose
+	 * NET_SKB_PAD, exceeds 64B. It should be 64B for 64-bit
+	 * platforms and 0B for 32-bit ones.
+	 */
+	pp->rx_offset_correction =
+		max(0, NET_SKB_PAD - MVNETA_RX_PKT_OFFSET_CORRECTION);
+
 	pp->indir[0] = rxq_def;
 
 	pp->clk = devm_clk_get(&pdev->dev, "core");