[PATCH net-next v1] net: stmmac: TSO: Simplify the code flow of DMA descriptor allocations

[Furong Xu <0x1207@gmail.com>]

The DMA AXI address width of DWMAC cores can be configured to
32-bit/40-bit/48-bit, then the format of DMA transmit descriptors
get a little different between 32-bit and 40-bit/48-bit.
Current driver code checks priv->dma_cap.addr64 to use certain format
with certain configuration.

This patch converts the format of DMA transmit descriptors on platforms
that the DMA AXI address width is configured to 32-bit (as described by
function comments of stmmac_tso_xmit() in current code) to a more generic
format (see the updated function comments after this patch) which is
actually already used on 40-bit/48-bit platforms to provide better
compatibility and make code flow cleaner.

Tested and verified on:
DWMAC CORE 5.10a with 32-bit DMA AXI address width
DWXGMAC CORE 3.20a with 40-bit DMA AXI address width

Signed-off-by: Furong Xu <0x1207@gmail.com>
---
 .../net/ethernet/stmicro/stmmac/stmmac_main.c | 60 ++++++++-----------
 1 file changed, 24 insertions(+), 36 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 16b8bcfa8b11..a48b7cf74a29 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -4121,11 +4121,7 @@ static void stmmac_tso_allocator(struct stmmac_priv *priv, dma_addr_t des,
 			desc = &tx_q->dma_tx[tx_q->cur_tx];
 
 		curr_addr = des + (total_len - tmp_len);
-		if (priv->dma_cap.addr64 <= 32)
-			desc->des0 = cpu_to_le32(curr_addr);
-		else
-			stmmac_set_desc_addr(priv, desc, curr_addr);
-
+		stmmac_set_desc_addr(priv, desc, curr_addr);
 		buff_size = tmp_len >= TSO_MAX_BUFF_SIZE ?
 			    TSO_MAX_BUFF_SIZE : tmp_len;
 
@@ -4171,17 +4167,27 @@ static void stmmac_flush_tx_descriptors(struct stmmac_priv *priv, int queue)
  *  First Descriptor
  *   --------
  *   | DES0 |---> buffer1 = L2/L3/L4 header
- *   | DES1 |---> TCP Payload (can continue on next descr...)
- *   | DES2 |---> buffer 1 and 2 len
+ *   | DES1 |---> can be used as buffer2 for TCP Payload if the DMA AXI address
+ *   |      |     width is 32-bit, but we never use it.
+ *   |      |     Also can be used as the most-significant 8-bits or 16-bits of
+ *   |      |     buffer1 address pointer if the DMA AXI address width is 40-bit
+ *   |      |     or 48-bit, and we always use it.
+ *   | DES2 |---> buffer1 len
  *   | DES3 |---> must set TSE, TCP hdr len-> [22:19]. TCP payload len [17:0]
  *   --------
+ *   --------
+ *   | DES0 |---> buffer1 = TCP Payload (can continue on next descr...)
+ *   | DES1 |---> same as the First Descriptor
+ *   | DES2 |---> buffer1 len
+ *   | DES3 |
+ *   --------
  *	|
  *     ...
  *	|
  *   --------
- *   | DES0 | --| Split TCP Payload on Buffers 1 and 2
- *   | DES1 | --|
- *   | DES2 | --> buffer 1 and 2 len
+ *   | DES0 |---> buffer1 = Split TCP Payload
+ *   | DES1 |---> same as the First Descriptor
+ *   | DES2 |---> buffer1 len
  *   | DES3 |
  *   --------
  *
@@ -4191,15 +4197,14 @@ static netdev_tx_t stmmac_tso_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct dma_desc *desc, *first, *mss_desc = NULL;
 	struct stmmac_priv *priv = netdev_priv(dev);
-	int tmp_pay_len = 0, first_tx, nfrags;
 	unsigned int first_entry, tx_packets;
 	struct stmmac_txq_stats *txq_stats;
 	struct stmmac_tx_queue *tx_q;
 	u32 pay_len, mss, queue;
-	dma_addr_t tso_des, des;
+	int i, first_tx, nfrags;
 	u8 proto_hdr_len, hdr;
+	dma_addr_t des;
 	bool set_ic;
-	int i;
 
 	/* Always insert VLAN tag to SKB payload for TSO frames.
 	 *
@@ -4284,24 +4289,9 @@ static netdev_tx_t stmmac_tso_xmit(struct sk_buff *skb, struct net_device *dev)
 	if (dma_mapping_error(priv->device, des))
 		goto dma_map_err;
 
-	if (priv->dma_cap.addr64 <= 32) {
-		first->des0 = cpu_to_le32(des);
-
-		/* Fill start of payload in buff2 of first descriptor */
-		if (pay_len)
-			first->des1 = cpu_to_le32(des + proto_hdr_len);
-
-		/* If needed take extra descriptors to fill the remaining payload */
-		tmp_pay_len = pay_len - TSO_MAX_BUFF_SIZE;
-		tso_des = des;
-	} else {
-		stmmac_set_desc_addr(priv, first, des);
-		tmp_pay_len = pay_len;
-		tso_des = des + proto_hdr_len;
-		pay_len = 0;
-	}
-
-	stmmac_tso_allocator(priv, tso_des, tmp_pay_len, (nfrags == 0), queue);
+	stmmac_set_desc_addr(priv, first, des);
+	stmmac_tso_allocator(priv, des + proto_hdr_len, pay_len,
+			     (nfrags == 0), queue);
 
 	/* In case two or more DMA transmit descriptors are allocated for this
 	 * non-paged SKB data, the DMA buffer address should be saved to
@@ -4405,11 +4395,9 @@ static netdev_tx_t stmmac_tso_xmit(struct sk_buff *skb, struct net_device *dev)
 	}
 
 	/* Complete the first descriptor before granting the DMA */
-	stmmac_prepare_tso_tx_desc(priv, first, 1,
-			proto_hdr_len,
-			pay_len,
-			1, tx_q->tx_skbuff_dma[first_entry].last_segment,
-			hdr / 4, (skb->len - proto_hdr_len));
+	stmmac_prepare_tso_tx_desc(priv, first, 1, proto_hdr_len, 0, 1,
+				   tx_q->tx_skbuff_dma[first_entry].last_segment,
+				   hdr / 4, (skb->len - proto_hdr_len));
 
 	/* If context desc is used to change MSS */
 	if (mss_desc) {
-- 
2.34.1