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@zii.aero>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/Documentation/devicetree/bindings/net/mdio.yaml b/Documentation/devicetree/bindings/net/mdio.yaml
index ab4a9df..cd6c6ae 100644 (file)
--- 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 832a24e..1ae075a 100644 (file)
--- 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 */