net: ethernet: adi: adin1110: Fix SPI transfers

No need to use more than one SPI transfer for reads.
Use only one from now as ADIN1110/2111 does not tolerate
CS changes during reads.

The BCM2711/2708 SPI controllers worked fine, but the NXP
IMX8MM could not keep CS lowered during SPI bursts.

This change aims to make the ADIN1110/2111 driver compatible
with both SPI controllers, without any loss of bandwidth/other
capabilities.

Fixes: bc93e19d ("net: ethernet: adi: Add ADIN1110 support")
Signed-off-by: Alexandru Tachici <alexandru.tachici@analog.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/adi/adin1110.c

@@ -196,7 +196,7 @@ static int adin1110_read_reg(struct adin1110_priv *priv, u16 reg, u32 *val)
 {
 	u32 header_len = ADIN1110_RD_HEADER_LEN;
 	u32 read_len = ADIN1110_REG_LEN;
-	struct spi_transfer t[2] = {0};
+	struct spi_transfer t = {0};
 	int ret;
 
 	priv->data[0] = ADIN1110_CD | FIELD_GET(GENMASK(12, 8), reg);
@@ -209,17 +209,15 @@ static int adin1110_read_reg(struct adin1110_priv *priv, u16 reg, u32 *val)
 		header_len++;
 	}
 
-	t[0].tx_buf = &priv->data[0];
-	t[0].len = header_len;
-
 	if (priv->append_crc)
 		read_len++;
 
 	memset(&priv->data[header_len], 0, read_len);
-	t[1].rx_buf = &priv->data[header_len];
-	t[1].len = read_len;
+	t.tx_buf = &priv->data[0];
+	t.rx_buf = &priv->data[0];
+	t.len = read_len + header_len;
 
-	ret = spi_sync_transfer(priv->spidev, t, 2);
+	ret = spi_sync_transfer(priv->spidev, &t, 1);
 	if (ret)
 		return ret;
 
@@ -296,7 +294,7 @@ static int adin1110_read_fifo(struct adin1110_port_priv *port_priv)
 {
 	struct adin1110_priv *priv = port_priv->priv;
 	u32 header_len = ADIN1110_RD_HEADER_LEN;
-	struct spi_transfer t[2] = {0};
+	struct spi_transfer t;
 	u32 frame_size_no_fcs;
 	struct sk_buff *rxb;
 	u32 frame_size;
@@ -327,12 +325,7 @@ static int adin1110_read_fifo(struct adin1110_port_priv *port_priv)
 		return ret;
 
 	frame_size_no_fcs = frame_size - ADIN1110_FRAME_HEADER_LEN - ADIN1110_FEC_LEN;
-
-	rxb = netdev_alloc_skb(port_priv->netdev, round_len);
-	if (!rxb)
-		return -ENOMEM;
-
-	memset(priv->data, 0, round_len + ADIN1110_RD_HEADER_LEN);
+	memset(priv->data, 0, ADIN1110_RD_HEADER_LEN);
 
 	priv->data[0] = ADIN1110_CD | FIELD_GET(GENMASK(12, 8), reg);
 	priv->data[1] = FIELD_GET(GENMASK(7, 0), reg);
@@ -342,21 +335,23 @@ static int adin1110_read_fifo(struct adin1110_port_priv *port_priv)
 		header_len++;
 	}
 
-	skb_put(rxb, frame_size_no_fcs + ADIN1110_FRAME_HEADER_LEN);
+	rxb = netdev_alloc_skb(port_priv->netdev, round_len + header_len);
+	if (!rxb)
+		return -ENOMEM;
 
-	t[0].tx_buf = &priv->data[0];
-	t[0].len = header_len;
+	skb_put(rxb, frame_size_no_fcs + header_len + ADIN1110_FRAME_HEADER_LEN);
 
-	t[1].rx_buf = &rxb->data[0];
-	t[1].len = round_len;
+	t.tx_buf = &priv->data[0];
+	t.rx_buf = &rxb->data[0];
+	t.len = header_len + round_len;
 
-	ret = spi_sync_transfer(priv->spidev, t, 2);
+	ret = spi_sync_transfer(priv->spidev, &t, 1);
 	if (ret) {
 		kfree_skb(rxb);
 		return ret;
 	}
 
-	skb_pull(rxb, ADIN1110_FRAME_HEADER_LEN);
+	skb_pull(rxb, header_len + ADIN1110_FRAME_HEADER_LEN);
 	rxb->protocol = eth_type_trans(rxb, port_priv->netdev);
 
 	if ((port_priv->flags & IFF_ALLMULTI && rxb->pkt_type == PACKET_MULTICAST) ||