net: phy: add I2C mdio bus

Add an I2C MDIO bus bridge library, to allow phylib to access PHYs which
are connected to an I2C bus instead of the more conventional MDIO bus.
Such PHYs can be found in SFP adapters and SFF modules.

Since PHYs appear at I2C bus address 0x40..0x5f, and 0x50/0x51 are
reserved for SFP EEPROMs/diagnostics, we must not allow the MDIO bus
to access these I2C addresses.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 109 insertions, 0 deletions

diff --git a/drivers/net/phy/mdio-i2c.c b/drivers/net/phy/mdio-i2c.c
new file mode 100644
index 000000000000..6d24fd13ca86
--- /dev/null
+++ b/drivers/net/phy/mdio-i2c.c
@@ -0,0 +1,109 @@
+/*
+ * MDIO I2C bridge
+ *
+ * Copyright (C) 2015-2016 Russell King
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * Network PHYs can appear on I2C buses when they are part of SFP module.
+ * This driver exposes these PHYs to the networking PHY code, allowing
+ * our PHY drivers access to these PHYs, and so allowing configuration
+ * of their settings.
+ */
+#include <linux/i2c.h>
+#include <linux/phy.h>
+
+#include "mdio-i2c.h"
+
+/*
+ * I2C bus addresses 0x50 and 0x51 are normally an EEPROM, which is
+ * specified to be present in SFP modules.  These correspond with PHY
+ * addresses 16 and 17.  Disallow access to these "phy" addresses.
+ */
+static bool i2c_mii_valid_phy_id(int phy_id)
+{
+	return phy_id != 0x10 && phy_id != 0x11;
+}
+
+static unsigned int i2c_mii_phy_addr(int phy_id)
+{
+	return phy_id + 0x40;
+}
+
+static int i2c_mii_read(struct mii_bus *bus, int phy_id, int reg)
+{
+	struct i2c_adapter *i2c = bus->priv;
+	struct i2c_msg msgs[2];
+	u8 data[2], dev_addr = reg;
+	int bus_addr, ret;
+
+	if (!i2c_mii_valid_phy_id(phy_id))
+		return 0xffff;
+
+	bus_addr = i2c_mii_phy_addr(phy_id);
+	msgs[0].addr = bus_addr;
+	msgs[0].flags = 0;
+	msgs[0].len = 1;
+	msgs[0].buf = &dev_addr;
+	msgs[1].addr = bus_addr;
+	msgs[1].flags = I2C_M_RD;
+	msgs[1].len = sizeof(data);
+	msgs[1].buf = data;
+
+	ret = i2c_transfer(i2c, msgs, ARRAY_SIZE(msgs));
+	if (ret != ARRAY_SIZE(msgs))
+		return 0xffff;
+
+	return data[0] << 8 | data[1];
+}
+
+static int i2c_mii_write(struct mii_bus *bus, int phy_id, int reg, u16 val)
+{
+	struct i2c_adapter *i2c = bus->priv;
+	struct i2c_msg msg;
+	int ret;
+	u8 data[3];
+
+	if (!i2c_mii_valid_phy_id(phy_id))
+		return 0;
+
+	data[0] = reg;
+	data[1] = val >> 8;
+	data[2] = val;
+
+	msg.addr = i2c_mii_phy_addr(phy_id);
+	msg.flags = 0;
+	msg.len = 3;
+	msg.buf = data;
+
+	ret = i2c_transfer(i2c, &msg, 1);
+
+	return ret < 0 ? ret : 0;
+}
+
+struct mii_bus *mdio_i2c_alloc(struct device *parent, struct i2c_adapter *i2c)
+{
+	struct mii_bus *mii;
+
+	if (!i2c_check_functionality(i2c, I2C_FUNC_I2C))
+		return ERR_PTR(-EINVAL);
+
+	mii = mdiobus_alloc();
+	if (!mii)
+		return ERR_PTR(-ENOMEM);
+
+	snprintf(mii->id, MII_BUS_ID_SIZE, "i2c:%s", dev_name(parent));
+	mii->parent = parent;
+	mii->read = i2c_mii_read;
+	mii->write = i2c_mii_write;
+	mii->priv = i2c;
+
+	return mii;
+}
+EXPORT_SYMBOL_GPL(mdio_i2c_alloc);
+
+MODULE_AUTHOR("Russell King");
+MODULE_DESCRIPTION("MDIO I2C bridge library");
+MODULE_LICENSE("GPL v2");