realtek: Add support for SFP EEPROM-access over SMBus

The EEPROMs on SFP modules are compatible both to I2C as well
as SMBus. However, the kernel so far only supports I2C
access. We add SMBus access routines, because the I2C driver
for the RTL9300 HW only supports that protocol. At the same
time we disable I2C access to PHYs on SFP modules as otherwise
detection of any SFP module would fail. This is not in any
way problematic at this point in time since the RTL93XX
platform so far does not support PHYs on SFP modules.

The patches are copied and rebased version of:
https://bootlin.com/blog/sfp-modules-on-a-board-running-linux/

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Signed-off-by: Birger Koblitz <git@birger-koblitz.de>

1 files changed, 99 insertions, 0 deletions

diff --git a/target/linux/realtek/patches-5.10/712-net-phy-sfp-add-support-for-SMBus.patch b/target/linux/realtek/patches-5.10/712-net-phy-sfp-add-support-for-SMBus.patch
new file mode 100644
index 0000000000..8eef1885ab
--- /dev/null
+++ b/target/linux/realtek/patches-5.10/712-net-phy-sfp-add-support-for-SMBus.patch
@@ -0,0 +1,99 @@
+From 3cb0bde365d913c484d20224367a54a0eac780a7 Mon Sep 17 00:00:00 2001
+From: Antoine Tenart <antoine.tenart@bootlin.com>
+Date: Fri, 21 Feb 2020 11:55:29 +0100
+Subject: [PATCH 3/3] net: phy: sfp: add support for SMBus
+
+Signed-off-by: Antoine Tenart <antoine.tenart@bootlin.com>
+---
+ drivers/net/phy/sfp.c | 68 ++++++++++++++++++++++++++++++++++---------
+ 1 file changed, 54 insertions(+), 14 deletions(-)
+
+--- a/drivers/net/phy/sfp.c
++++ b/drivers/net/phy/sfp.c
+@@ -412,32 +412,72 @@ static int sfp_i2c_write(struct sfp *sfp
+ 	return ret == ARRAY_SIZE(msgs) ? len : 0;
+ }
+ 
++static int sfp_smbus_read(struct sfp *sfp, bool a2, u8 dev_addr, void *buf,
++			  size_t len)
++{
++	u8 bus_addr = a2 ? 0x51 : 0x50, *val = buf;
++
++	bus_addr -= 0x40;
++
++	while (len > 0) {
++		*val = sfp->i2c_mii->read(sfp->i2c_mii, bus_addr, dev_addr);
++
++		val++;
++		dev_addr++;
++		len--;
++	}
++
++	return val - (u8 *)buf;
++}
++
++static int sfp_smbus_write(struct sfp *sfp, bool a2, u8 dev_addr, void *buf,
++			   size_t len)
++{
++	u8 bus_addr = a2 ? 0x51 : 0x50;
++	u16 val;
++
++	memcpy(&val, buf, len);
++
++	return sfp->i2c_mii->write(sfp->i2c_mii, bus_addr, dev_addr, val);
++}
++
+ static int sfp_i2c_configure(struct sfp *sfp, struct i2c_adapter *i2c)
+ {
+-	struct mii_bus *i2c_mii;
++	struct mii_bus *mii;
+ 	int ret;
+ 
+-	if (!i2c_check_functionality(i2c, I2C_FUNC_I2C))
+-		return -EINVAL;
+-
+ 	sfp->i2c = i2c;
+-	sfp->read = sfp_i2c_read;
+-	sfp->write = sfp_i2c_write;
+ 
+-	i2c_mii = mdio_i2c_alloc(sfp->dev, i2c);
+-	if (IS_ERR(i2c_mii))
+-		return PTR_ERR(i2c_mii);
++	if (i2c_check_functionality(i2c, I2C_FUNC_I2C)) {
++		sfp->read = sfp_i2c_read;
++		sfp->write = sfp_i2c_write;
++
++		mii = mdio_i2c_alloc(sfp->dev, i2c);
++		if (IS_ERR(mii))
++			return PTR_ERR(mii);
++
++		mii->name = "SFP I2C Bus";
++	} else if (i2c_check_functionality(i2c, I2C_FUNC_SMBUS_BYTE_DATA)) {
++		sfp->read = sfp_smbus_read;
++		sfp->write = sfp_smbus_write;
++
++		mii = mdio_smbus_alloc(sfp->dev, i2c);
++		if (IS_ERR(mii))
++			return PTR_ERR(mii);
+ 
+-	i2c_mii->name = "SFP I2C Bus";
+-	i2c_mii->phy_mask = ~0;
++		mii->name = "SFP SMBus";
++	} else {
++		return -EINVAL;
++	}
+ 
+-	ret = mdiobus_register(i2c_mii);
++	mii->phy_mask = ~0;
++	ret = mdiobus_register(mii);
+ 	if (ret < 0) {
+-		mdiobus_free(i2c_mii);
++		mdiobus_free(mii);
+ 		return ret;
+ 	}
+ 
+-	sfp->i2c_mii = i2c_mii;
++	sfp->i2c_mii = mii;
+ 
+ 	return 0;
+ }