netdev - [PATCH net-next v2 3/3] net: ethernet: fec: Allow the MDIO preamble to be disabled

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Date:   Sat, 18 Apr 2020 02:03:55 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     David Miller <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>, fugang.duan@....com,
        Andrew Lunn <andrew@...n.ch>,
        Chris Healy <Chris.Healy@....aero>
Subject: [PATCH net-next v2 3/3] net: ethernet: fec: Allow the MDIO preamble to be disabled

An MDIO transaction normally starts with 32 1s as a preamble. However
not all devices requires such a preamble. Add a device tree property
which allows the preamble to be suppressed. This will half the size of
the MDIO transaction, allowing faster transactions.

Suggested-by: Chris Healy <Chris.Healy@....aero>
Signed-off-by: Andrew Lunn <andrew@...n.ch>
---
 Documentation/devicetree/bindings/net/mdio.yaml | 4 ++++
 drivers/net/ethernet/freescale/fec_main.c       | 9 ++++++++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/net/mdio.yaml b/Documentation/devicetree/bindings/net/mdio.yaml
index bcd457c54cd7..41ed4019f8ca 100644
--- a/Documentation/devicetree/bindings/net/mdio.yaml
+++ b/Documentation/devicetree/bindings/net/mdio.yaml
@@ -43,6 +43,10 @@ properties:
     description:
       Desired MDIO bus clock frequency in Hz.
 
+  suppress-preamble:
+        description: The 32 bit preamble should be suppressed.
+        type: boolean
+
 patternProperties:
   "^ethernet-phy@[0-9a-f]+$":
     type: object
diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
index 28ef0abfa660..3404e085c657 100644
--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c
@@ -2064,6 +2064,7 @@ static int fec_enet_mii_init(struct platform_device *pdev)
 	static struct mii_bus *fec0_mii_bus;
 	struct net_device *ndev = platform_get_drvdata(pdev);
 	struct fec_enet_private *fep = netdev_priv(ndev);
+	bool suppress_preamble = false;
 	struct device_node *node;
 	int err = -ENXIO;
 	u32 mii_speed, holdtime;
@@ -2097,8 +2098,11 @@ static int fec_enet_mii_init(struct platform_device *pdev)
 
 	bus_freq = 2500000; /* 2.5MHz by default */
 	node = of_get_child_by_name(pdev->dev.of_node, "mdio");
-	if (node)
+	if (node) {
 		of_property_read_u32(node, "clock-frequency", &bus_freq);
+		suppress_preamble = of_property_read_bool(node,
+							  "suppress-preamble");
+	}
 
 	/*
 	 * Set MII speed (= clk_get_rate() / 2 * phy_speed)
@@ -2135,6 +2139,9 @@ static int fec_enet_mii_init(struct platform_device *pdev)
 
 	fep->phy_speed = mii_speed << 1 | holdtime << 8;
 
+	if (suppress_preamble)
+		fep->phy_speed |= BIT(7);
+
 	writel(fep->phy_speed, fep->hwp + FEC_MII_SPEED);
 
 	/* Clear any pending transaction complete indication */
-- 
2.26.1