Subject: [PATCH 2/2] net: stmmac: support shared MDIO

From: Bartosz Golaszewski <[email-masked]>
Date: Mon, 7 Aug 2023 21:31:02 +0200

From: Bartosz Golaszewski <[email-masked]>

When two MACs share the MDIO lines to their respective PHYs, one is
considered the logical "owner" of the bus. The secondary controller must
wait until the MDIO bus is registered before trying to attach to the
PHY.

If the mdio node is not defined for given MAC, try to read the
"snps,shared-mdio" property on its node. If it exists, parse the phandle
and store the result as the MAC's mdio device-tree node.

When registering the MDIO bus: if we know that we share it with another
MAC, lookup the MDIO bus and if it's not up yet, defer probe until it
is.

Signed-off-by: Bartosz Golaszewski <[email-masked]>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_mdio.c     | 8 ++++++++
 drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c | 6 ++++++
 include/linux/stmmac.h                                | 1 +
 3 files changed, 15 insertions(+)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_mdio.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_mdio.c
index dd9e2fec5328..6a74b91595d0 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_mdio.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_mdio.c
@@ -543,6 +543,14 @@ int stmmac_mdio_register(struct net_device *ndev)
 	if (!mdio_bus_data)
 		return 0;
 
+	if (priv->plat->flags & STMMAC_FLAG_SHARED_MDIO) {
+		new_bus = of_mdio_find_bus(mdio_node);
+		if (!new_bus)
+			return -EPROBE_DEFER;
+
+		goto bus_register_done;
+	}
+
 	new_bus = mdiobus_alloc();
 	if (!new_bus)
 		return -ENOMEM;
diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c
index be8e79c7aa34..11a24b1c7beb 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c
@@ -340,6 +340,12 @@ static int stmmac_dt_phy(struct plat_stmmacenet_data *plat,
 		}
 	}
 
+	if (!plat->mdio_node) {
+		plat->mdio_node = of_parse_phandle(np, "snps,shared-mdio", 0);
+		if (plat->mdio_node)
+			plat->flags |= STMMAC_FLAG_SHARED_MDIO;
+	}
+
 	if (plat->mdio_node) {
 		dev_dbg(dev, "Found MDIO subnode\n");
 		mdio = true;
diff --git a/include/linux/stmmac.h b/include/linux/stmmac.h
index 3d0702510224..892f61051002 100644
--- a/include/linux/stmmac.h
+++ b/include/linux/stmmac.h
@@ -218,6 +218,7 @@ struct dwmac4_addrs {
 #define STMMAC_FLAG_INT_SNAPSHOT_EN		BIT(9)
 #define STMMAC_FLAG_RX_CLK_RUNS_IN_LPI		BIT(10)
 #define STMMAC_FLAG_EN_TX_LPI_CLOCKGATING	BIT(11)
+#define STMMAC_FLAG_SHARED_MDIO			BIT(12)
 
 struct plat_stmmacenet_data {
 	int bus_id;
-- 
2.39.2