Merge branch 'net-phy-sfp-add-single-byte-smbus-sfp-access'

Maxime Chevallier says:

====================
net: phy: sfp: Add single-byte SMBus SFP access

This is V4 for the single-byte SMBus support for SFP cages as well as
embedded PHYs accessed over mdio-i2c.

v3: https://lore.kernel.org/20250314162319.516163-1-maxime.chevallier@bootlin.com
v2: https://lore.kernel.org/20250225112043.419189-1-maxime.chevallier@bootlin.com
v1: https://lore.kernel.org/20250223172848.1098621-1-maxime.chevallier@bootlin.com
====================

Link: https://patch.msgid.link/20250322075745.120831-1-maxime.chevallier@bootlin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

2 files changed, 152 insertions, 9 deletions

diff --git a/drivers/net/mdio/mdio-i2c.c b/drivers/net/mdio/mdio-i2c.c
index da2001ea1f99..53e96bfab542 100644
--- a/drivers/net/mdio/mdio-i2c.c
+++ b/drivers/net/mdio/mdio-i2c.c
@@ -106,6 +106,62 @@ static int i2c_mii_write_default_c22(struct mii_bus *bus, int phy_id, int reg,
 	return i2c_mii_write_default_c45(bus, phy_id, -1, reg, val);
 }
 
+static int smbus_byte_mii_read_default_c22(struct mii_bus *bus, int phy_id,
+					   int reg)
+{
+	struct i2c_adapter *i2c = bus->priv;
+	union i2c_smbus_data smbus_data;
+	int val = 0, ret;
+
+	if (!i2c_mii_valid_phy_id(phy_id))
+		return 0;
+
+	ret = i2c_smbus_xfer(i2c, i2c_mii_phy_addr(phy_id), 0,
+			     I2C_SMBUS_READ, reg,
+			     I2C_SMBUS_BYTE_DATA, &smbus_data);
+	if (ret < 0)
+		return ret;
+
+	val = (smbus_data.byte & 0xff) << 8;
+
+	ret = i2c_smbus_xfer(i2c, i2c_mii_phy_addr(phy_id), 0,
+			     I2C_SMBUS_READ, reg,
+			     I2C_SMBUS_BYTE_DATA, &smbus_data);
+	if (ret < 0)
+		return ret;
+
+	val |= smbus_data.byte & 0xff;
+
+	return val;
+}
+
+static int smbus_byte_mii_write_default_c22(struct mii_bus *bus, int phy_id,
+					    int reg, u16 val)
+{
+	struct i2c_adapter *i2c = bus->priv;
+	union i2c_smbus_data smbus_data;
+	int ret;
+
+	if (!i2c_mii_valid_phy_id(phy_id))
+		return 0;
+
+	smbus_data.byte = (val & 0xff00) >> 8;
+
+	ret = i2c_smbus_xfer(i2c, i2c_mii_phy_addr(phy_id), 0,
+			     I2C_SMBUS_WRITE, reg,
+			     I2C_SMBUS_BYTE_DATA, &smbus_data);
+	if (ret < 0)
+		return ret;
+
+	smbus_data.byte = val & 0xff;
+
+	ret = i2c_smbus_xfer(i2c, i2c_mii_phy_addr(phy_id), 0,
+			     I2C_SMBUS_WRITE, reg,
+			     I2C_SMBUS_BYTE_DATA, &smbus_data);
+
+	return ret < 0 ? ret : 0;
+}
+
 /* RollBall SFPs do not access internal PHY via I2C address 0x56, but
  * instead via address 0x51, when SFP page is set to 0x03 and password to
  * 0xffffffff.
@@ -378,13 +434,26 @@ static int i2c_mii_init_rollball(struct i2c_adapter *i2c)
 		return 0;
 }
 
+static bool mdio_i2c_check_functionality(struct i2c_adapter *i2c,
+					 enum mdio_i2c_proto protocol)
+{
+	if (i2c_check_functionality(i2c, I2C_FUNC_I2C))
+		return true;
+
+	if (i2c_check_functionality(i2c, I2C_FUNC_SMBUS_BYTE_DATA) &&
+	    protocol == MDIO_I2C_MARVELL_C22)
+		return true;
+
+	return false;
+}
+
 struct mii_bus *mdio_i2c_alloc(struct device *parent, struct i2c_adapter *i2c,
 			       enum mdio_i2c_proto protocol)
 {
 	struct mii_bus *mii;
 	int ret;
 
-	if (!i2c_check_functionality(i2c, I2C_FUNC_I2C))
+	if (!mdio_i2c_check_functionality(i2c, protocol))
 		return ERR_PTR(-EINVAL);
 
 	mii = mdiobus_alloc();
@@ -395,6 +464,14 @@ struct mii_bus *mdio_i2c_alloc(struct device *parent, struct i2c_adapter *i2c,
 	mii->parent = parent;
 	mii->priv = i2c;
 
+	/* Only use SMBus if we have no other choice */
+	if (i2c_check_functionality(i2c, I2C_FUNC_SMBUS_BYTE_DATA) &&
+	    !i2c_check_functionality(i2c, I2C_FUNC_I2C)) {
+		mii->read = smbus_byte_mii_read_default_c22;
+		mii->write = smbus_byte_mii_write_default_c22;
+		return mii;
+	}
+
 	switch (protocol) {
 	case MDIO_I2C_ROLLBALL:
 		ret = i2c_mii_init_rollball(i2c);
diff --git a/drivers/net/phy/sfp.c b/drivers/net/phy/sfp.c
index c88217af44a1..347c1e0e94d9 100644
--- a/drivers/net/phy/sfp.c
+++ b/drivers/net/phy/sfp.c
@@ -234,6 +234,7 @@ struct sfp {
 	enum mdio_i2c_proto mdio_protocol;
 	struct phy_device *mod_phy;
 	const struct sff_data *type;
+	size_t i2c_max_block_size;
 	size_t i2c_block_size;
 	u32 max_power_mW;
 
@@ -691,14 +692,71 @@ static int sfp_i2c_write(struct sfp *sfp, bool a2, u8 dev_addr, void *buf,
 	return ret == ARRAY_SIZE(msgs) ? len : 0;
 }
 
-static int sfp_i2c_configure(struct sfp *sfp, struct i2c_adapter *i2c)
+static int sfp_smbus_byte_read(struct sfp *sfp, bool a2, u8 dev_addr,
+			       void *buf, size_t len)
 {
-	if (!i2c_check_functionality(i2c, I2C_FUNC_I2C))
-		return -EINVAL;
+	union i2c_smbus_data smbus_data;
+	u8 bus_addr = a2 ? 0x51 : 0x50;
+	u8 *data = buf;
+	int ret;
+
+	while (len) {
+		ret = i2c_smbus_xfer(sfp->i2c, bus_addr, 0,
+				     I2C_SMBUS_READ, dev_addr,
+				     I2C_SMBUS_BYTE_DATA, &smbus_data);
+		if (ret < 0)
+			return ret;
+
+		*data = smbus_data.byte;
+
+		len--;
+		data++;
+		dev_addr++;
+	}
+
+	return data - (u8 *)buf;
+}
+
+static int sfp_smbus_byte_write(struct sfp *sfp, bool a2, u8 dev_addr,
+				void *buf, size_t len)
+{
+	union i2c_smbus_data smbus_data;
+	u8 bus_addr = a2 ? 0x51 : 0x50;
+	u8 *data = buf;
+	int ret;
 
+	while (len) {
+		smbus_data.byte = *data;
+		ret = i2c_smbus_xfer(sfp->i2c, bus_addr, 0,
+				     I2C_SMBUS_WRITE, dev_addr,
+				     I2C_SMBUS_BYTE_DATA, &smbus_data);
+		if (ret)
+			return ret;
+
+		len--;
+		data++;
+		dev_addr++;
+	}
+
+	return 0;
+}
+
+static int sfp_i2c_configure(struct sfp *sfp, struct i2c_adapter *i2c)
+{
 	sfp->i2c = i2c;
-	sfp->read = sfp_i2c_read;
-	sfp->write = sfp_i2c_write;
+
+	if (i2c_check_functionality(i2c, I2C_FUNC_I2C)) {
+		sfp->read = sfp_i2c_read;
+		sfp->write = sfp_i2c_write;
+		sfp->i2c_max_block_size = SFP_EEPROM_BLOCK_SIZE;
+	} else if (i2c_check_functionality(i2c, I2C_FUNC_SMBUS_BYTE_DATA)) {
+		sfp->read = sfp_smbus_byte_read;
+		sfp->write = sfp_smbus_byte_write;
+		sfp->i2c_max_block_size = 1;
+	} else {
+		sfp->i2c = NULL;
+		return -EINVAL;
+	}
 
 	return 0;
 }
@@ -1594,7 +1652,7 @@ static void sfp_hwmon_probe(struct work_struct *work)
 	 */
 	if (sfp->i2c_block_size < 2) {
 		dev_info(sfp->dev,
-			 "skipping hwmon device registration due to broken EEPROM\n");
+			 "skipping hwmon device registration\n");
 		dev_info(sfp->dev,
 			 "diagnostic EEPROM area cannot be read atomically to guarantee data coherency\n");
 		return;
@@ -2201,7 +2259,7 @@ static int sfp_sm_mod_probe(struct sfp *sfp, bool report)
 	u8 check;
 	int ret;
 
-	sfp->i2c_block_size = SFP_EEPROM_BLOCK_SIZE;
+	sfp->i2c_block_size = sfp->i2c_max_block_size;
 
 	ret = sfp_read(sfp, false, 0, &id.base, sizeof(id.base));
 	if (ret < 0) {
@@ -2941,7 +2999,6 @@ static struct sfp *sfp_alloc(struct device *dev)
 		return ERR_PTR(-ENOMEM);
 
 	sfp->dev = dev;
-	sfp->i2c_block_size = SFP_EEPROM_BLOCK_SIZE;
 
 	mutex_init(&sfp->sm_mutex);
 	mutex_init(&sfp->st_mutex);
@@ -3115,6 +3172,15 @@ static int sfp_probe(struct platform_device *pdev)
 	if (!sfp->sfp_bus)
 		return -ENOMEM;
 
+	if (sfp->i2c_max_block_size < 2)
+		dev_warn(sfp->dev,
+			 "Please note:\n"
+			 "This SFP cage is accessed via an SMBus only capable of single byte\n"
+			 "transactions. Some features are disabled, other may be unreliable or\n"
+			 "sporadically fail. Use with caution. There is nothing that the kernel\n"
+			 "or community can do to fix it, the kernel will try best efforts. Please\n"
+			 "verify any problems on hardware that supports multi-byte I2C transactions.\n");
+
 	sfp_debugfs_init(sfp);
 
 	return 0;