In commit d4bd3aca33c2 ("net: mdio: mdio-i2c: Add support for single-byte SMBus operations"), we introduced single-byte SMBus support for the mdio-i2c. This was intended to deal with the case where the I2C adapter that accesses the SFP module is limited to single-byte smbus accesses. We find this type of adapters in some PHY devices such as the VSC8552. It was discovered that some SFP modules have a built-in PHY that only reply to single-byte smbus accesses. This is the case for the Prolabs GLC-GE-100FX-C SGMII to 100FX module, which contains a Broadcom BCM5461 PHY. In that case, trying to access the PHY with regular 16-bit transactions with the mdio-i2c driver causes the PHY to stall the i2c bus completely, without any way to recover. Accessing it in single-byte mode however, works fine. Add a dedicated MDIO_I2C_SINGLE_BYTE_C22 protocol type, so that we can setup the mdio-i2c driver accordingly. The good news here is that this should work on pretty much every setup, as a true I2C adapter is also capable of single-byte accesses thanks to the i2c smbus emulation layer. Some care will need to be taken should we add support for word-only smbus adapters. Signed-off-by: Maxime Chevallier --- drivers/net/mdio/mdio-i2c.c | 12 ++++++++---- drivers/net/phy/sfp.c | 1 + include/linux/mdio/mdio-i2c.h | 1 + 3 files changed, 10 insertions(+), 4 deletions(-) diff --git a/drivers/net/mdio/mdio-i2c.c b/drivers/net/mdio/mdio-i2c.c index ed20352a589a..86ae8a5c0ebd 100644 --- a/drivers/net/mdio/mdio-i2c.c +++ b/drivers/net/mdio/mdio-i2c.c @@ -452,7 +452,8 @@ static bool mdio_i2c_check_functionality(struct i2c_adapter *i2c, return true; if (i2c_check_functionality(i2c, I2C_FUNC_SMBUS_BYTE_DATA) && - protocol == MDIO_I2C_MARVELL_C22) + (protocol == MDIO_I2C_MARVELL_C22 || + protocol == MDIO_I2C_SINGLE_BYTE_C22)) return true; return false; @@ -475,9 +476,12 @@ 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)) { + /* Only use single-byte SMBus if explicitly asked, or if we have no + * other choice. + */ + if (protocol == MDIO_I2C_SINGLE_BYTE_C22 || + (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; diff --git a/drivers/net/phy/sfp.c b/drivers/net/phy/sfp.c index 1f9112efef62..bff91735f681 100644 --- a/drivers/net/phy/sfp.c +++ b/drivers/net/phy/sfp.c @@ -2016,6 +2016,7 @@ static int sfp_sm_probe_for_phy(struct sfp *sfp) break; case MDIO_I2C_MARVELL_C22: + case MDIO_I2C_SINGLE_BYTE_C22: err = sfp_sm_probe_phy(sfp, SFP_PHY_ADDR, false); break; diff --git a/include/linux/mdio/mdio-i2c.h b/include/linux/mdio/mdio-i2c.h index 65b550a6fc32..f51c474da5b1 100644 --- a/include/linux/mdio/mdio-i2c.h +++ b/include/linux/mdio/mdio-i2c.h @@ -16,6 +16,7 @@ enum mdio_i2c_proto { MDIO_I2C_MARVELL_C22, MDIO_I2C_C45, MDIO_I2C_ROLLBALL, + MDIO_I2C_SINGLE_BYTE_C22, }; struct mii_bus *mdio_i2c_alloc(struct device *parent, struct i2c_adapter *i2c, -- 2.49.0