netdev - [PATCH net-next v3 3/3] net: ethernet: fec: Allow the MDIO preamble to be disabled

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Date:   Mon, 20 Apr 2020 00:04:02 +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 v3 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. But it should only
be used when all devices on the bus support suppressed preamble.

Suggested-by: Chris Healy <Chris.Healy@....aero>
Signed-off-by: Andrew Lunn <andrew@...n.ch>
Reviewed-by: Florian Fainelli <f.fainelli@...il.com>
---
 Documentation/devicetree/bindings/net/mdio.yaml | 6 ++++++
 drivers/net/ethernet/freescale/fec_main.c       | 9 ++++++++-
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/net/mdio.yaml b/Documentation/devicetree/bindings/net/mdio.yaml
index ab4a9df8b8e2..cd6c6ae6dabb 100644
--- a/Documentation/devicetree/bindings/net/mdio.yaml
+++ b/Documentation/devicetree/bindings/net/mdio.yaml
@@ -45,6 +45,12 @@ properties:
       defined 2.5MHz should only be used when all devices on the bus support
       the given clock speed.
 
+  suppress-preamble:
+    description:
+      The 32 bit preamble should be suppressed. In order for this to
+      work, all devices on the bus must support suppressed preamble.
+    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 832a24e2805c..1ae075a246a3 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