[PATCH net-next v2 04/14] net: pcs: xpcs: re-order xpcs_pre_config() to update after the reset

[Alex Elder <elder@riscstar.com>]

From: Daniel Thompson <daniel@riscstar.com>

Currently, on Wangxun platforms, the XPCS is configured during the call
to xpcs_switch_interface_mode() and, if the need_reset flag is set, the
XPCS is reset and the configuration will be lost. This is harmless at
present because need_reset will never actually be set on these platforms.

Nevertheless having xpcs_switch_interface_mode() on the wrong side of
the reset is an obstacle for future changes where wiping out programmed
configuration with a reset could be harmful.

Reorder xpcs_pre_config() to allow the reset can happen before we
switch interface mode. To make this work we have to hoist the special
case logic for SGMII into the parent function.

Signed-off-by: Daniel Thompson <daniel@riscstar.com>
Signed-off-by: Alex Elder <elder@riscstar.com>
---
 drivers/net/pcs/pcs-xpcs.c | 56 ++++++++++++++++++++------------------
 1 file changed, 30 insertions(+), 26 deletions(-)

diff --git a/drivers/net/pcs/pcs-xpcs.c b/drivers/net/pcs/pcs-xpcs.c
index e69fa2f0a0e8d..76c04372b5b50 100644
--- a/drivers/net/pcs/pcs-xpcs.c
+++ b/drivers/net/pcs/pcs-xpcs.c
@@ -705,46 +705,50 @@ static void xpcs_get_interfaces(struct dw_xpcs *xpcs, unsigned long *interfaces)
 static int xpcs_switch_interface_mode(struct dw_xpcs *xpcs,
 				      phy_interface_t interface)
 {
-	int ret = 0;
+	/* Wangxun provides a full alternative implementation to handle quirks */
+	if (xpcs->info.pma == WX_TXGBE_XPCS_PMA_10G_ID)
+		return txgbe_xpcs_switch_mode(xpcs, interface);
 
-	if (xpcs->info.pma == WX_TXGBE_XPCS_PMA_10G_ID) {
-		ret = txgbe_xpcs_switch_mode(xpcs, interface);
-	} else if (xpcs->interface != interface) {
-		if (interface == PHY_INTERFACE_MODE_SGMII)
-			xpcs->need_reset = true;
-		xpcs->interface = interface;
-	}
+	xpcs->interface = interface;
 
-	return ret;
+	return 0;
 }
 
 static void xpcs_pre_config(struct phylink_pcs *pcs, phy_interface_t interface)
 {
 	struct dw_xpcs *xpcs = phylink_pcs_to_xpcs(pcs);
 	const struct dw_xpcs_compat *compat;
+	bool force_reset;
 	int ret;
 
+	/*
+	 * According to the XPCS datasheet, a soft reset is required to initiate
+	 * Clause 37 auto-negotiation when the XPCS switches interface modes.
+	 */
+	force_reset = interface == PHY_INTERFACE_MODE_SGMII;
+
+	if (force_reset || xpcs->need_reset) {
+		compat = xpcs_find_compat(xpcs, interface);
+		if (!compat) {
+			dev_err(&xpcs->mdiodev->dev, "unsupported interface %s\n",
+				phy_modes(interface));
+			return;
+		}
+
+		ret = xpcs_soft_reset(xpcs, compat);
+		if (ret) {
+			dev_err(&xpcs->mdiodev->dev, "soft reset failed: %pe\n",
+				ERR_PTR(ret));
+			return;
+		}
+
+		xpcs->need_reset = false;
+	}
+
 	ret = xpcs_switch_interface_mode(xpcs, interface);
 	if (ret)
 		dev_err(&xpcs->mdiodev->dev, "switch interface failed: %pe\n",
 			ERR_PTR(ret));
-
-	if (!xpcs->need_reset)
-		return;
-
-	compat = xpcs_find_compat(xpcs, interface);
-	if (!compat) {
-		dev_err(&xpcs->mdiodev->dev, "unsupported interface %s\n",
-			phy_modes(interface));
-		return;
-	}
-
-	ret = xpcs_soft_reset(xpcs, compat);
-	if (ret)
-		dev_err(&xpcs->mdiodev->dev, "soft reset failed: %pe\n",
-			ERR_PTR(ret));
-
-	xpcs->need_reset = false;
 }
 
 static int xpcs_config_aneg_c37_sgmii(struct dw_xpcs *xpcs,
-- 
2.51.0