RE: [Patch net-next 4/4] net: fec: Workaround for imx6sx enet tx hang when enable three queues

From: Shawn Guo <redacted> Sent: Tuesday, September 16, 2014 8:52 AM

To: Li Frank-B20596
Cc: Duan Fugang-B38611; davem@davemloft.net; netdev@vger.kernel.org;
lznuaa@gmail.com; linux-arm-kernel@lists.infradead.org
Subject: Re: [Patch net-next 4/4] net: fec: Workaround for imx6sx enet tx
hang when enable three queues

On Tue, Sep 16, 2014 at 01:12:57AM +0800, Frank.Li@freescale.com wrote:

quoted

From: Fugang Duan <redacted>

When enable three queues on imx6sx enet, and then do tx performance
test with iperf tool, after some time running, tx hang.

Found that:
	If uDMA is running, software set TDAR may cause tx hang.
	If uDMA is in idle, software set TDAR don't cause tx hang.

There is a TDAR race condition for mutliQ when the software sets TDAR
and the UDMA clears TDAR simultaneously or in a small window (2-4

cycles).

quoted

This will cause the udma_tx and udma_tx_arbiter state machines to hang.
The issue exist at i.MX6SX enet IP.

So, the Workaround is checking TDAR status four time, if TDAR cleared
by hardware and then write TDAR, otherwise don't set TDAR.

The patch is only one Workaround for the issue TKT210582.

Signed-off-by: Fugang Duan <redacted>
Signed-off-by: Frank Li <redacted>
---
 drivers/net/ethernet/freescale/fec_main.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/freescale/fec_main.c

b/drivers/net/ethernet/freescale/fec_main.c
index 524ddbe..452e576 100644

--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c

@@ -111,6 +111,13 @@ static void fec_enet_itr_coal_init(struct

net_device *ndev);

quoted

  *   independent rings
  */
 #define FEC_QUIRK_HAS_AVB		(1 << 8)
+/*
+ * There is a TDAR race condition for mutliQ when the software sets
+TDAR
+ * and the UDMA clears TDAR simultaneously or in a small window (2-4

cycles).

quoted

+ * This will cause the udma_tx and udma_tx_arbiter state machines to

hang.

quoted

+ * The issue exist at i.MX6SX enet IP.
+ */
+#define FEC_QUIRK_TKT210582		(1 << 9)

I think TKTxxx number is used by Freescale design team to track issues
internally, and there should be a corresponding errata number like ERRxxx
which should be accessible by external people in errata document?

Shawn

The issue ticket is: TDAR race condition for mutliQ - Errata: ERR007885

quoted

 static struct platform_device_id fec_devtype[] = {
 	{

@@ -139,7 +146,7 @@ static struct platform_device_id fec_devtype[] = {
 		.driver_data = FEC_QUIRK_ENET_MAC | FEC_QUIRK_HAS_GBIT |
 				FEC_QUIRK_HAS_BUFDESC_EX | FEC_QUIRK_HAS_CSUM |
 				FEC_QUIRK_HAS_VLAN | FEC_QUIRK_ERR006358 |
-				FEC_QUIRK_HAS_AVB,
+				FEC_QUIRK_HAS_AVB | FEC_QUIRK_TKT210582,
 	}, {
 		/* sentinel */
 	}

@@ -709,6 +716,8 @@ static int fec_enet_txq_submit_tso(struct

fec_enet_priv_tx_q *txq,

quoted

 	struct tso_t tso;
 	unsigned int index = 0;
 	int ret;
+	const struct platform_device_id *id_entry =
+				platform_get_device_id(fep->pdev);

 	if (tso_count_descs(skb) >= fec_enet_get_free_txdesc_num(fep, txq))

{

quoted

 		dev_kfree_skb_any(skb);

@@ -770,7 +779,12 @@ static int fec_enet_txq_submit_tso(struct

fec_enet_priv_tx_q *txq,

quoted

 	txq->cur_tx = bdp;

 	/* Trigger transmission start */
-	writel(0, fep->hwp + FEC_X_DES_ACTIVE(queue));
+	if (!(id_entry->driver_data & FEC_QUIRK_TKT210582) ||
+		!readl(fep->hwp + FEC_X_DES_ACTIVE(queue)) ||
+		!readl(fep->hwp + FEC_X_DES_ACTIVE(queue)) ||
+		!readl(fep->hwp + FEC_X_DES_ACTIVE(queue)) ||
+		!readl(fep->hwp + FEC_X_DES_ACTIVE(queue)))
+		writel(0, fep->hwp + FEC_X_DES_ACTIVE(queue));

 	return 0;

--
1.9.1