[PATCH net-next 0/2] net: pcs: xpcs: fix operating mode selection

[PATCH net-next 0/2] net: pcs: xpcs: fix operating mode selection

[Alex Elder]

The XPCS found on Toshiba TC9564 is unable to operate at 2500base-X
and slower with a PHY connected using SGMII/2500base-X.  This XPCS
supports 10Gbase-R, which is the default operating mode, and this
causes mode selection to fail for slower interfaces (SGMII, 1000baseX,
and 2500baseX).  Writing a reserved value to the MDIO_CTRL2 register
avoids this failure.

Wangxun already addresses a similar scenario, but includes custom
quirk handling.

This series implements handling for slower rates for an XPCS that
supports 10Gbase-R.  The first patch rearranges code that performs
soft reset so that it is done *before* the interface mode is
switched.  The second adds code to xpcs_switch_interface_mode()
to update the MDIO_CTRL2 register for interfaces that support
10Gbase-R so that the desired rate change works as intended.

					-Alex

Daniel Thompson (2):
  net: pcs: xpcs: re-order xpcs_pre_config() to update after the reset
  net: pcs: xpcs: select operating mode for 10G-baseR capable PCS

 drivers/net/pcs/pcs-xpcs.c | 94 +++++++++++++++++++++++++++-----------
 1 file changed, 67 insertions(+), 27 deletions(-)


base-commit: 05b5019b01fb9443b09ae4ed34af1135a80a84c8
-- 
2.53.0

[PATCH net-next 1/2] net: pcs: xpcs: re-order xpcs_pre_config() to update after the reset

[Alex Elder]

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() so 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>
Co-developed-by: Alex Elder <elder@riscstar.com>
Signed-off-by: Alex Elder <elder@riscstar.com>
---
 drivers/net/pcs/pcs-xpcs.c | 59 ++++++++++++++++++++------------------
 1 file changed, 31 insertions(+), 28 deletions(-)

diff --git a/drivers/net/pcs/pcs-xpcs.c b/drivers/net/pcs/pcs-xpcs.c
index b415b93d77c15..49abf5ea6f5cc 100644
--- a/drivers/net/pcs/pcs-xpcs.c
+++ b/drivers/net/pcs/pcs-xpcs.c
@@ -705,46 +705,49 @@ 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);
+	struct device *dev = &xpcs->mdiodev->dev;
 	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(dev, "unsupported interface %s\n",
+				phy_modes(interface));
+			return;
+		}
+
+		ret = xpcs_soft_reset(xpcs, compat);
+		if (ret) {
+			dev_err(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;
+		dev_err(dev, "switch interface failed: %pe\n", ERR_PTR(ret));
 }
 
 static int xpcs_config_aneg_c37_sgmii(struct dw_xpcs *xpcs,
-- 
2.53.0

[PATCH net-next 2/2] net: pcs: xpcs: select operating mode for 10G-baseR capable PCS

[Alex Elder]

From: Daniel Thompson <daniel@riscstar.com>

Currently the XPCS found on Toshiba TC9564 is unable to operate at
2500base-X and slower with a PHY connected using SGMII/2500base-X
(in our case a Qualcomm QCA8081).

The problem arises because this XPCS supports 10Gbase-R. That means
that the reset value of SR_XS_PCS_CTRL2:PCS_TYPE_SEL (0) is valid and
this suppresses the modal switching based on bit 13 of SR_PMA_CTRL1
or SR_XS_PCS_CTRL1.

A fix for this behaviour is implemented by txgbe_xpcs_switch_mode()
as part of the quirks for WangXun devices.

Rather than introduce another quirk for TC9564 let's attempt so solve
this generically by setting SR_XS_PCS_CTRL2:PCS_TYPE_SEL to a reserved
value when we detect the right combination of phy interface and XPCS
feature support.

The generic strategy adopted requires the default value of PCS_TYPE_SEL
to be 0 on devices that support 10Gbase-R. Based on TC9564 documentation
and the logic already implemented for WangXun I believe this is likely
to be the case for currently supported XPCS devices. Sadly I don't have
access to generic XPCS docs to confirm. However I think the benefits
of avoiding a cargo culted quirk outweighs the risk of regression.

Signed-off-by: Daniel Thompson <daniel@riscstar.com>
Co-developed-by: Alex Elder <elder@riscstar.com>
Signed-off-by: Alex Elder <elder@riscstar.com>
---
 drivers/net/pcs/pcs-xpcs.c | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/drivers/net/pcs/pcs-xpcs.c b/drivers/net/pcs/pcs-xpcs.c
index 49abf5ea6f5cc..5316cf9c31f19 100644
--- a/drivers/net/pcs/pcs-xpcs.c
+++ b/drivers/net/pcs/pcs-xpcs.c
@@ -705,10 +705,47 @@ 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 mdio_stat2, ret;
+
 	/* 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);
 
+	mdio_stat2 = xpcs_read(xpcs, MDIO_MMD_PCS, MDIO_STAT2);
+	if (mdio_stat2 < 0)
+		return mdio_stat2;
+
+	/*
+	 * If this XPCS supports 10Gbase-R then that will be the default
+	 * operating mode. There are several interface modes where this default
+	 * is unhelpful. Change the operating mode for interfaces were we know
+	 * the default is wrong, and restore the default otherwise.
+	 */
+	if (mdio_stat2 & MDIO_PCS_STAT2_10GBR) {
+		switch (interface) {
+		case PHY_INTERFACE_MODE_SGMII:
+		case PHY_INTERFACE_MODE_1000BASEX:
+		case PHY_INTERFACE_MODE_2500BASEX:
+			/*
+			 * Why are we writing MDIO_PCS_CTRL2_TYPE + 1? We want
+			 * the modal behaviour that comes when we pick a
+			 * reserved value. XPCS allocates extra bits to this
+			 * field and allocates values from 15 down so
+			 * MDIO_PCS_CTRL2_TYPE + 1 is the value likely to be
+			 * allocated last (and hopefully never).
+			 */
+			ret = xpcs_write(xpcs, MDIO_MMD_PCS, MDIO_CTRL2,
+					 MDIO_PCS_CTRL2_TYPE + 1);
+			break;
+		default:
+			ret = xpcs_write(xpcs, MDIO_MMD_PCS, MDIO_CTRL2,
+					 MDIO_PCS_CTRL2_10GBR);
+			break;
+		}
+		if (ret < 0)
+			return ret;
+	}
+
 	xpcs->interface = interface;
 
 	return 0;
-- 
2.53.0