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net: ethernet: fec: Allow the MDIO preamble to be disabled

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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>
This commit is contained in:
Andrew Lunn 2020-04-20 00:04:02 +02:00 committed by David S. Miller
parent 3e782985cb
commit 3c01eb62d1
2 changed files with 14 additions and 1 deletions
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6
Documentation/devicetree/bindings/net/mdio.yaml
View file

@ -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

9
drivers/net/ethernet/freescale/fec_main.c
View file

@ -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 */