netdev - [net-next PATCH v5 4/9] net: pcs: xpcs: Add support for FBNIC 25G, 50G, 100G PMD

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Message-ID: 
 <176374321695.959489.6648161125012056619.stgit@ahduyck-xeon-server.home.arpa>
Date: Fri, 21 Nov 2025 08:40:16 -0800
From: Alexander Duyck <alexander.duyck@...il.com>
To: netdev@...r.kernel.org
Cc: kuba@...nel.org, kernel-team@...a.com, andrew+netdev@...n.ch,
 hkallweit1@...il.com, linux@...linux.org.uk, pabeni@...hat.com,
 davem@...emloft.net
Subject: [net-next PATCH v5 4/9] net: pcs: xpcs: Add support for FBNIC 25G,
 50G, 100G PMD

From: Alexander Duyck <alexanderduyck@...com>

The fbnic driver is planning to make use of the XPCS driver to enable
support for PCS and better integration with phylink. To do this though we
will need to enable several workarounds since the PMD interface for fbnic
is likely to be unique since it is a mix of two different vendor products
with a unique wrapper around the IP.

I have generated a PHY identifier based on IEEE 802.3-2022 22.2.4.3.1 using
an OUI belonging to Meta Platforms and used with our NICs. Using this we
will provide it as the PMD ID via the SW based MDIO interface so that
the fbnic device can be identified and necessary workarounds enabled in the
XPCS driver.

As an initial workaround this change adds an exception so that soft_reset
is not set when the driver is initially bound to the PCS.

In addition I have added logic to integrate the PMD Rx signal detect state
into the link state for the PCS. With this we can avoid the link coming up
too soon on the FBNIC PMD and as a result of it being in the training state
so we can avoid link flaps.

Signed-off-by: Alexander Duyck <alexanderduyck@...com>
---
 drivers/net/pcs/pcs-xpcs.c   |   24 ++++++++++++++++++++++--
 include/linux/pcs/pcs-xpcs.h |    2 ++
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/drivers/net/pcs/pcs-xpcs.c b/drivers/net/pcs/pcs-xpcs.c
index a94a7cb93664..9679f2b35a44 100644
--- a/drivers/net/pcs/pcs-xpcs.c
+++ b/drivers/net/pcs/pcs-xpcs.c
@@ -597,7 +597,26 @@ static int xpcs_c45_read_pcs_speed(struct dw_xpcs *xpcs,
 static int xpcs_resolve_pma(struct dw_xpcs *xpcs,
 			    struct phylink_link_state *state)
 {
-	int err = 0;
+	int pmd_rxdet, err = 0;
+
+	/* The Meta Platforms FBNIC PMD will go into a training state for
+	 * about 4 seconds when the link first comes up. During this time the
+	 * PCS link will bounce. To avoid reporting link up too soon we include
+	 * the PMD state provided by the driver.
+	 */
+	if (xpcs->info.pma == MP_FBNIC_XPCS_PMA_100G_ID) {
+		pmd_rxdet = xpcs_read(xpcs, MDIO_MMD_PMAPMD, MDIO_PMA_RXDET);
+		if (pmd_rxdet < 0) {
+			state->link = false;
+			return pmd_rxdet;
+		}
+
+		/* Verify Rx lanes are trained before reporting link up */
+		if (!(pmd_rxdet & MDIO_PMD_RXDET_GLOBAL)) {
+			state->link = false;
+			return 0;
+		}
+	}
 
 	state->pause = MLO_PAUSE_TX | MLO_PAUSE_RX;
 	state->duplex = DUPLEX_FULL;
@@ -1591,7 +1610,8 @@ static struct dw_xpcs *xpcs_create(struct mdio_device *mdiodev)
 
 	xpcs_get_interfaces(xpcs, xpcs->pcs.supported_interfaces);
 
-	if (xpcs->info.pma == WX_TXGBE_XPCS_PMA_10G_ID)
+	if (xpcs->info.pma == WX_TXGBE_XPCS_PMA_10G_ID ||
+	    xpcs->info.pma == MP_FBNIC_XPCS_PMA_100G_ID)
 		xpcs->pcs.poll = false;
 	else
 		xpcs->need_reset = true;
diff --git a/include/linux/pcs/pcs-xpcs.h b/include/linux/pcs/pcs-xpcs.h
index 4cf6bd611e5a..36073f7b6bb4 100644
--- a/include/linux/pcs/pcs-xpcs.h
+++ b/include/linux/pcs/pcs-xpcs.h
@@ -39,6 +39,8 @@ enum dw_xpcs_pma_id {
 	DW_XPCS_PMA_GEN5_10G_ID,
 	DW_XPCS_PMA_GEN5_12G_ID,
 	WX_TXGBE_XPCS_PMA_10G_ID = 0xfc806000,
+	/* Meta Platforms OUI 88:25:08, model 0, revision 0 */
+	MP_FBNIC_XPCS_PMA_100G_ID = 0x46904000,
 };
 
 struct dw_xpcs_info {