[PATCH net-next 02/12] net: pcs: pcs-xpcs: select operating mode for 10G-baseR capable PCS

[Alex Elder <elder@riscstar.com>]

From: Daniel Thompson <daniel@riscstar.com>

Currently the XPCS found on Toshiba TC9564 (a.k.a. Qualcomm QPS615)
is unable to operate at 1000base-X and slower with a PHY connected
using SGMII/2500base-X (in our case a Qualcomm QCA8081).

The problem arises when the 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.

The reported XPCS dev ID on a TC9564 is exactly the same as every other
XPCS supported by the kernel so we can't use the dev ID to automatically
determine what operating mode to select. However we can use the feature
bits in SR_XS_PCS_STS2 to detect 10Gbase-R support.

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

Signed-off-by: Daniel Thompson <daniel@riscstar.com>
Signed-off-by: Alex Elder <elder@riscstar.com>
---
 drivers/net/pcs/pcs-xpcs.c | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/drivers/net/pcs/pcs-xpcs.c b/drivers/net/pcs/pcs-xpcs.c
index e69fa2f0a0e8d..b2c84b7e1e113 100644
--- a/drivers/net/pcs/pcs-xpcs.c
+++ b/drivers/net/pcs/pcs-xpcs.c
@@ -747,6 +747,40 @@ static void xpcs_pre_config(struct phylink_pcs *pcs, phy_interface_t interface)
 	xpcs->need_reset = false;
 }
 
+static int xpcs_config_operating_mode(struct dw_xpcs *xpcs, int an_mode)
+{
+	int mdio_stat2, ret;
+
+	switch (an_mode) {
+	case DW_AN_C37_SGMII:
+	case DW_AN_C37_1000BASEX:
+	case DW_2500BASEX:
+		mdio_stat2 = xpcs_read(xpcs, MDIO_MMD_PCS, MDIO_STAT2);
+		if (mdio_stat2 < 0)
+			return mdio_stat2;
+
+		/*
+		 * If this XPCS supports 10Gbase-R then it will be the default
+		 * which prevents 1000base-X and slower from working correctly.
+		 *
+		 * 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).
+		 */
+		if (mdio_stat2 & MDIO_PCS_STAT2_10GBR) {
+			ret = xpcs_write(xpcs, MDIO_MMD_PCS, MDIO_CTRL2,
+					 MDIO_PCS_CTRL2_TYPE + 1);
+			if (ret < 0)
+				return ret;
+		}
+		break;
+	}
+
+	return 0;
+}
+
 static int xpcs_config_aneg_c37_sgmii(struct dw_xpcs *xpcs,
 				      unsigned int neg_mode)
 {
@@ -919,6 +953,10 @@ static int xpcs_do_config(struct dw_xpcs *xpcs, phy_interface_t interface,
 	if (!compat)
 		return -ENODEV;
 
+	ret = xpcs_config_operating_mode(xpcs, compat->an_mode);
+	if (ret < 0)
+		return ret;
+
 	if (xpcs->info.pma == WX_TXGBE_XPCS_PMA_10G_ID) {
 		/* Wangxun devices need backplane CL37 AN enabled for
 		 * SGMII and 1000base-X
-- 
2.51.0