net: xilinx: axiethernet: Add check for transmit data FIFO vacancy

In a scenario when the multiple iperf3 transmit streams are executed there
is a high probability to overflow the transmit FIFO buffer and generate
async abort(SError) which might lead to kernel panic.

In the transmit path, add proper locking to ensure updates to TX FIFO
are atomic and also check transmit data FIFO vacancy before writing to
the TX FIFO. This is inline with recommended programming sequence for
transmitting a packet using axistream FIFO and as a side effect it also
fixes the below iperf3 crash:

[ 283.692957] SError Interrupt on CPU1, code 0xbf000002 – SError
[ 283.692960] CPU: 1 PID: 515 Comm: udhcpc Not tainted 5.4.0-xilinx-v2020.1 #1
[ 283.692961] Hardware name: xlnx,zynqmp (DT)
[ 283.692963] pstate: 80000085 (Nzcv daIf -PAN -UAO)
[ 283.692964] pc : dma_direct_map_page+0x20/0x130
[ 283.692966] lr : axienet_start_xmit+0x1ac/0x6b0
[ 283.692967] sp : ffffffc01000b860
[ 283.692968] x29: ffffffc01000b860 x28: 0000000000000001
[ 283.692971] x27: ffffffc0112c5400 x26: ffffff8876f047c0
[ 283.692974] x25: ffffffc0112c5000 x24: 0000000000000000
[ 283.692977] x23: ffffff8876f04000 x22: 0000000000000000
[ 283.692980] x21: ffffffc0112c5400 x20: ffffff8876012700
[ 283.692983] x19: ffffff887ab48c10 x18: 0000000000000000
[ 283.692985] x17: 0000000000000000 x16: 0000000000000000
[ 283.692988] x15: 0000000000000000 x14: 0000000000000000
[ 283.692991] x13: 0000000000000000 x12: 0000000000000000
[ 283.692994] x11: 0000000000000000 x10: 0000000000000000
[ 283.692997] x9 : 0000000000000000 x8 : 0000000000000000
[ 283.693000] x7 : 0000000000000000 x6 : fffffffeffe00000
[ 283.693002] x5 : 0000000000000000 x4 : 0000000000000001
[ 283.693005] x3 : 00000000000005ea x2 : 00000000000000ce
[ 283.693008] x1 : 0000000021d86040 x0 : ffffff887ab48c10
[ 283.693012] SError Interrupt on CPU2, code 0xbf000002 – SError
[ 283.693014] CPU: 2 PID: 622 Comm: iperf3 Not tainted 5.4.0-xilinx-v2020.1 #1
[ 283.693015] Hardware name: xlnx,zynqmp (DT)
[ 283.693016] pstate: 80000085 (Nzcv daIf -PAN -UAO)
[ 283.693018] pc : dma_direct_map_page+0x20/0x130
[ 283.693019] lr : axienet_start_xmit+0x1ac/0x6b0
[ 283.693020] sp : ffffffc011d4b4a0
[ 283.693021] x29: ffffffc011d4b4a0 x28: 0000000000000001
[ 283.693024] x27: ffffffc01130dd80 x26: ffffff8876f047c0

Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>
Reviewed-by: Harini Katakam <harini.katakam@xilinx.com>
State: pending

drivers/net/ethernet/xilinx/xilinx_axienet.h

@@ -155,6 +155,7 @@
 
 /* AXI Tx Timestamp Stream FIFO Register Definitions */
 #define XAXIFIFO_TXTS_ISR	0x00000000 /* Interrupt Status Register */
+#define XAXIFIFO_TXTS_TDFV	0x0000000C /* Transmit Data FIFO Vacancy */
 #define XAXIFIFO_TXTS_TXFD	0x00000010 /* Tx Data Write Port */
 #define XAXIFIFO_TXTS_TLR	0x00000014 /* Transmit Length Register */
 #define XAXIFIFO_TXTS_RFO	0x0000001C /* Rx Fifo Occupancy */
@@ -798,9 +799,9 @@ struct axienet_local {
 	u8  ptp_rx_sw_pointer;
 	struct sk_buff_head ptp_txq;
 	struct work_struct tx_tstamp_work;
-	spinlock_t ptp_tx_lock;		/* TSN PTP tx lock*/
 #endif
 #endif
+	spinlock_t ptp_tx_lock;		/* PTP tx lock*/
 	int eth_irq;
 
 	u32 options;			/* Current options word */

drivers/net/ethernet/xilinx/xilinx_axienet_main.c

@@ -1094,10 +1094,11 @@ static inline int axienet_check_tx_bd_space(struct axienet_dma_q *q,
  * @buf:	Pointer to the buf to copy timestamp header
  * @msg_type:	PTP message type
  *
- * Return:	None.
+ * Return: 0, on success
+ *	    NETDEV_TX_BUSY, if timestamp FIFO has no vacancy
  */
-static void axienet_create_tsheader(u8 *buf, u8 msg_type,
-				    struct axienet_dma_q *q)
+static int axienet_create_tsheader(u8 *buf, u8 msg_type,
+				   struct axienet_dma_q *q)
 {
 	struct axienet_local *lp = q->lp;
 #ifdef CONFIG_AXIENET_HAS_MCDMA
@@ -1107,6 +1108,7 @@ static void axienet_create_tsheader(u8 *buf, u8 msg_type,
 #endif
 	u64 val;
 	u32 tmp;
+	u32 flags;
 
 #ifdef CONFIG_AXIENET_HAS_MCDMA
 	cur_p = &q->txq_bd_v[q->tx_bd_tail];
@@ -1135,9 +1137,19 @@ static void axienet_create_tsheader(u8 *buf, u8 msg_type,
 	} else if (lp->axienet_config->mactype == XAXIENET_10G_25G ||
 		   lp->axienet_config->mactype == XAXIENET_MRMAC) {
 		memcpy(&tmp, buf, XXVENET_TS_HEADER_LEN);
+		/* Check for Transmit Data FIFO Vacancy */
+		spin_lock_irqsave(&lp->ptp_tx_lock, flags);
+		if (!axienet_txts_ior(lp, XAXIFIFO_TXTS_TDFV)) {
+			spin_unlock_irqrestore(&lp->ptp_tx_lock, flags);
+			return NETDEV_TX_BUSY;
+		}
 		axienet_txts_iow(lp, XAXIFIFO_TXTS_TXFD, tmp);
-		axienet_txts_iow(lp, XAXIFIFO_TXTS_TLR, XXVENET_TS_HEADER_LEN);
+		axienet_txts_iow(lp, XAXIFIFO_TXTS_TLR,
+				 XXVENET_TS_HEADER_LEN);
+		spin_unlock_irqrestore(&lp->ptp_tx_lock, flags);
 	}
+
+	return 0;
 }
 #endif
 
@@ -1262,19 +1274,24 @@ static int axienet_skb_tstsmp(struct sk_buff **__skb, struct axienet_dma_q *q,
 			dev_dbg(lp->dev, "tx_tag:[%04x]\n",
 				cur_p->ptp_tx_ts_tag);
 			if (lp->tstamp_config.tx_type == HWTSTAMP_TX_ONESTEP_SYNC) {
-				axienet_create_tsheader(lp->tx_ptpheader,
-							TX_TS_OP_ONESTEP, q);
+				if (axienet_create_tsheader(lp->tx_ptpheader,
+							    TX_TS_OP_ONESTEP,
+							    q))
+					return NETDEV_TX_BUSY;
 			} else {
-				axienet_create_tsheader(lp->tx_ptpheader,
-							TX_TS_OP_TWOSTEP, q);
+				if (axienet_create_tsheader(lp->tx_ptpheader,
+							    TX_TS_OP_TWOSTEP,
+							    q))
+					return NETDEV_TX_BUSY;
 				skb_shinfo(skb)->tx_flags |= SKBTX_IN_PROGRESS;
 				cur_p->ptp_tx_skb = (phys_addr_t)skb_get(skb);
 			}
 	} else if (lp->axienet_config->mactype == XAXIENET_10G_25G ||
 		   lp->axienet_config->mactype == XAXIENET_MRMAC) {
 			dev_dbg(lp->dev, "tx_tag:NOOP\n");
-			axienet_create_tsheader(lp->tx_ptpheader,
-						TX_TS_OP_NOOP, q);
+			if (axienet_create_tsheader(lp->tx_ptpheader,
+						    TX_TS_OP_NOOP, q))
+				return NETDEV_TX_BUSY;
 	}
 
 	return NETDEV_TX_OK;
@@ -3473,6 +3490,7 @@ static int axienet_probe(struct platform_device *pdev)
 			lp->tx_ptpheader = devm_kzalloc(&pdev->dev,
 						XXVENET_TS_HEADER_LEN,
 						GFP_KERNEL);
+			spin_lock_init(&lp->ptp_tx_lock);
 		}
 
 		of_node_put(np);