LPDC link stability fix - EP MDIO read race condition

Since driver reads periodically MDIO registers (timer function to check link state) and HAL reads periodically LPDC MDIO registers (through ioctl call) it happened once in a while that ioctl read operation would be interleaved with timer function. As a result HAL would get the value read from a different MDIO register than the one requested. This had caused occasional link restarts on LPDC ports.

LPDC link stability fix - EP MDIO read race condition
Since driver reads periodically MDIO registers (timer function to check link state) and HAL reads periodically LPDC MDIO registers (through ioctl call) it happened once in a while that ioctl read operation would be interleaved with timer function. As a result HAL would get the value read from a different MDIO register than the one requested. This had caused occasional link restarts on LPDC ports.
f8febec6 · Grzegorz Daniluk · 5f2b50fc · f8febec6
Commit f8febec6 authored Mar 12, 2020 by Grzegorz Daniluk
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Showing with 29 additions and 3 deletions

endpoint.c kernel/wr_nic/endpoint.c +29 -3

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--- a/kernel/wr_nic/endpoint.c
+++ b/kernel/wr_nic/endpoint.c
@@ -54,6 +54,7 @@ int wrn_phy_read(struct net_device *dev, int phy_id, int location)
 {
 	struct wrn_ep *ep = netdev_priv(dev);
 	u32 val;
+  int ctrl_adr, retries;

 	if (WR_IS_NODE) {
 		/*
@@ -65,10 +66,31 @@ int wrn_phy_read(struct net_device *dev, int phy_id, int location)
 		return -1;
 	}

-	wrn_ep_write(ep, MDIO_CR, EP_MDIO_CR_ADDR_W(location));
+  /* First check if there is previous MDIO operation still ongoing */
 	while( (wrn_ep_read(ep, MDIO_ASR) & EP_MDIO_ASR_READY) == 0)
-		;
-	val = wrn_ep_read(ep, MDIO_ASR);
+    ;
+
+  retries = 100;
+  while(retries > 0) {
+	  wrn_ep_write(ep, MDIO_CR, EP_MDIO_CR_ADDR_W(location));
+	  while( (wrn_ep_read(ep, MDIO_ASR) & EP_MDIO_ASR_READY) == 0)
+	  	;
+	  val = wrn_ep_read(ep, MDIO_ASR);
+
+    /* control read from MDIO_CR to be sure we read value from requested
+     * register */
+    ctrl_adr = EP_MDIO_CR_ADDR_R(wrn_ep_read(ep, MDIO_CR));
+    if (ctrl_adr == location)
+      break;
+    else {
+      /* there was a conflict, retry the read */
+      retries--;
+    }
+  }
+  /* If we got here with retries == 0, this means the read failed... */
+  if (retries == 0) {
+    printk("%s readout error on port wri%d\n", __func__, ep->ep_number + 1);
+  }
 	/* mask from wbgen macros */
 	return EP_MDIO_ASR_RDATA_R(val);
 }
@@ -88,6 +110,10 @@ void wrn_phy_write(struct net_device *dev, int phy_id, int location,
 		return;
 	}

+  /* First check if there is previous MDIO operation still ongoing */
+	while( (wrn_ep_read(ep, MDIO_ASR) & EP_MDIO_ASR_READY) == 0)
+    ;
+
 	wrn_ep_write(ep, MDIO_CR,
 		     EP_MDIO_CR_ADDR_W(location)
 		     | EP_MDIO_CR_DATA_W(value)