net: pcs: xpcs: avoid reading STAT1 more than once

Avoid reading the STAT1 registers more than once while getting the PCS
state, as this register contains latching-low bits that are lost after
the first read.
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/pcs/pcs-xpcs.c

@@ -271,15 +271,12 @@ static int xpcs_soft_reset(struct dw_xpcs *xpcs,
 })
 
 static int xpcs_read_fault_c73(struct dw_xpcs *xpcs,
-			       struct phylink_link_state *state)
+			       struct phylink_link_state *state,
+			       u16 pcs_stat1)
 {
 	int ret;
 
-	ret = xpcs_read(xpcs, MDIO_MMD_PCS, MDIO_STAT1);
-	if (ret < 0)
-		return ret;
-
-	if (ret & MDIO_STAT1_FAULT) {
+	if (pcs_stat1 & MDIO_STAT1_FAULT) {
 		xpcs_warn(xpcs, state, "Link fault condition detected!\n");
 		return -EFAULT;
 	}
@@ -321,21 +318,6 @@ static int xpcs_read_fault_c73(struct dw_xpcs *xpcs,
 	return 0;
 }
 
-static int xpcs_read_link_c73(struct dw_xpcs *xpcs)
-{
-	bool link = true;
-	int ret;
-
-	ret = xpcs_read(xpcs, MDIO_MMD_PCS, MDIO_STAT1);
-	if (ret < 0)
-		return ret;
-
-	if (!(ret & MDIO_STAT1_LSTATUS))
-		link = false;
-
-	return link;
-}
-
 static void xpcs_config_usxgmii(struct dw_xpcs *xpcs, int speed)
 {
 	int ret, speed_sel;
@@ -462,15 +444,11 @@ static int xpcs_config_aneg_c73(struct dw_xpcs *xpcs,
 
 static int xpcs_aneg_done_c73(struct dw_xpcs *xpcs,
 			      struct phylink_link_state *state,
-			      const struct xpcs_compat *compat)
+			      const struct xpcs_compat *compat, u16 an_stat1)
 {
 	int ret;
 
-	ret = xpcs_read(xpcs, MDIO_MMD_AN, MDIO_STAT1);
-	if (ret < 0)
-		return ret;
-
-	if (ret & MDIO_AN_STAT1_COMPLETE) {
+	if (an_stat1 & MDIO_AN_STAT1_COMPLETE) {
 		ret = xpcs_read(xpcs, MDIO_MMD_AN, MDIO_AN_LPA);
 		if (ret < 0)
 			return ret;
@@ -488,16 +466,12 @@ static int xpcs_aneg_done_c73(struct dw_xpcs *xpcs,
 }
 
 static int xpcs_read_lpa_c73(struct dw_xpcs *xpcs,
-			     struct phylink_link_state *state)
+			     struct phylink_link_state *state, u16 an_stat1)
 {
 	u16 lpa[3];
 	int i, ret;
 
-	ret = xpcs_read(xpcs, MDIO_MMD_AN, MDIO_STAT1);
-	if (ret < 0)
-		return ret;
-
-	if (!(ret & MDIO_AN_STAT1_LPABLE)) {
+	if (!(an_stat1 & MDIO_AN_STAT1_LPABLE)) {
 		phylink_clear(state->lp_advertising, Autoneg);
 		return 0;
 	}
@@ -880,13 +854,25 @@ static int xpcs_get_state_c73(struct dw_xpcs *xpcs,
 			      const struct xpcs_compat *compat)
 {
 	bool an_enabled;
+	int pcs_stat1;
+	int an_stat1;
 	int ret;
 
+	/* The link status bit is latching-low, so it is important to
+	 * avoid unnecessary re-reads of this register to avoid missing
+	 * a link-down event.
+	 */
+	pcs_stat1 = xpcs_read(xpcs, MDIO_MMD_PCS, MDIO_STAT1);
+	if (pcs_stat1 < 0) {
+		state->link = false;
+		return pcs_stat1;
+	}
+
 	/* Link needs to be read first ... */
-	state->link = xpcs_read_link_c73(xpcs) > 0 ? 1 : 0;
+	state->link = !!(pcs_stat1 & MDIO_STAT1_LSTATUS);
 
 	/* ... and then we check the faults. */
-	ret = xpcs_read_fault_c73(xpcs, state);
+	ret = xpcs_read_fault_c73(xpcs, state, pcs_stat1);
 	if (ret) {
 		ret = xpcs_soft_reset(xpcs, compat);
 		if (ret)
@@ -897,15 +883,38 @@ static int xpcs_get_state_c73(struct dw_xpcs *xpcs,
 		return xpcs_do_config(xpcs, state->interface, MLO_AN_INBAND, NULL);
 	}
 
+	/* There is no point doing anything else if the link is down. */
+	if (!state->link)
+		return 0;
+
 	an_enabled = linkmode_test_bit(ETHTOOL_LINK_MODE_Autoneg_BIT,
 				       state->advertising);
-	if (an_enabled && xpcs_aneg_done_c73(xpcs, state, compat)) {
-		state->an_complete = true;
-		xpcs_read_lpa_c73(xpcs, state);
+	if (an_enabled) {
+		/* The link status bit is latching-low, so it is important to
+		 * avoid unnecessary re-reads of this register to avoid missing
+		 * a link-down event.
+		 */
+		an_stat1 = xpcs_read(xpcs, MDIO_MMD_AN, MDIO_STAT1);
+		if (an_stat1 < 0) {
+			state->link = false;
+			return an_stat1;
+		}
+
+		state->an_complete = xpcs_aneg_done_c73(xpcs, state, compat,
+							an_stat1);
+		if (!state->an_complete) {
+			state->link = false;
+			return 0;
+		}
+
+		ret = xpcs_read_lpa_c73(xpcs, state, an_stat1);
+		if (ret < 0) {
+			state->link = false;
+			return ret;
+		}
+
 		phylink_resolve_c73(state);
-	} else if (an_enabled) {
-		state->link = 0;
-	} else if (state->link) {
+	} else {
 		xpcs_resolve_pma(xpcs, state);
 	}