[PATCH v2] net: sfp: add SMBus I2C block support
From: Jonas Jelonek <jelonek.jonas@gmail.com>
Date: 2026-01-05 15:47:14
Also in:
lkml
Subsystem:
ethernet phy library, networking drivers, sff/sfp/sfp+ module support, the rest · Maintainers:
Andrew Lunn, Heiner Kallweit, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Russell King, Linus Torvalds
Commit 7662abf4db94 ("net: phy: sfp: Add support for SMBus module access")
added support for SMBus-only controllers for module access. However,
this is restricted to single-byte accesses and has the implication that
hwmon is disabled (due to missing atomicity of 16-bit accesses) and
warnings are printed.
There are probably a lot of SMBus-only I2C controllers out in the wild
which support block reads. Right now, they don't work with SFP modules.
This applies - amongst others - to I2C/SMBus-only controllers in Realtek
longan and mango SoCs.
Downstream in OpenWrt, a patch similar to the abovementioned patch is
used for current LTS kernel 6.12. However, this uses byte-access for all
kinds of access and thus disregards the atomicity for wider access.
Introduce read/write SMBus I2C block operations to support SMBus-only
controllers with appropriate support for block read/write. Those
operations are used for all accesses if supported, otherwise the
single-byte operations will be used. With block reads, atomicity for
16-bit reads as required by hwmon is preserved and thus, hwmon can be
used.
The implementation requires the I2C_FUNC_SMBUS_I2C_BLOCK to be
supported as it relies on reading a pre-defined amount of bytes.
This isn't intended by the official SMBus Block Read but supported by
several I2C controllers/drivers.
Support for word access is not implemented due to issues regarding
endianness.
Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>
---
v2: return number of written bytes in sfp_smbus_block_write
v1: https://lore.kernel.org/netdev/20251228213331.472887-1-jelonek.jonas@gmail.com/ (local)
---
drivers/net/phy/sfp.c | 77 +++++++++++++++++++++++++++++++++++++++++--
1 file changed, 75 insertions(+), 2 deletions(-)
diff --git a/drivers/net/phy/sfp.c b/drivers/net/phy/sfp.c
index 6166e9196364..4f2175397534 100644
--- a/drivers/net/phy/sfp.c
+++ b/drivers/net/phy/sfp.c@@ -744,6 +744,35 @@ static int sfp_smbus_byte_read(struct sfp *sfp, bool a2, u8 dev_addr, return data - (u8 *)buf; } +static int sfp_smbus_block_read(struct sfp *sfp, bool a2, u8 dev_addr, + void *buf, size_t len) +{ + size_t block_size = sfp->i2c_block_size; + union i2c_smbus_data smbus_data; + u8 bus_addr = a2 ? 0x51 : 0x50; + u8 *data = buf; + u8 this_len; + int ret; + + while (len) { + this_len = min(len, block_size); + + smbus_data.block[0] = this_len; + ret = i2c_smbus_xfer(sfp->i2c, bus_addr, 0, + I2C_SMBUS_READ, dev_addr, + I2C_SMBUS_I2C_BLOCK_DATA, &smbus_data); + if (ret < 0) + return ret; + + memcpy(data, &smbus_data.block[1], this_len); + len -= this_len; + data += this_len; + dev_addr += this_len; + } + + return data - (u8 *)buf; +} + static int sfp_smbus_byte_write(struct sfp *sfp, bool a2, u8 dev_addr, void *buf, size_t len) {
@@ -765,26 +794,70 @@ static int sfp_smbus_byte_write(struct sfp *sfp, bool a2, u8 dev_addr, dev_addr++; } + return data - (u8 *)buf; +} + +static int sfp_smbus_block_write(struct sfp *sfp, bool a2, u8 dev_addr, + void *buf, size_t len) +{ + size_t block_size = sfp->i2c_block_size; + union i2c_smbus_data smbus_data; + u8 bus_addr = a2 ? 0x51 : 0x50; + u8 *data = buf; + u8 this_len; + int ret; + + while (len) { + this_len = min(len, block_size); + + smbus_data.block[0] = this_len; + memcpy(&smbus_data.block[1], data, this_len); + ret = i2c_smbus_xfer(sfp->i2c, bus_addr, 0, + I2C_SMBUS_WRITE, dev_addr, + I2C_SMBUS_I2C_BLOCK_DATA, &smbus_data); + if (ret) + return ret; + + len -= this_len; + data += this_len; + dev_addr += this_len; + } + return 0; } static int sfp_i2c_configure(struct sfp *sfp, struct i2c_adapter *i2c) { + size_t max_block_size; + sfp->i2c = i2c; 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; + max_block_size = SFP_EEPROM_BLOCK_SIZE; + } else if (i2c_check_functionality(i2c, I2C_FUNC_SMBUS_I2C_BLOCK)) { + sfp->read = sfp_smbus_block_read; + sfp->write = sfp_smbus_block_write; + + max_block_size = SFP_EEPROM_BLOCK_SIZE; + if (i2c->quirks && i2c->quirks->max_read_len) + max_block_size = min(max_block_size, + i2c->quirks->max_read_len); + if (i2c->quirks && i2c->quirks->max_write_len) + max_block_size = min(max_block_size, + i2c->quirks->max_write_len); + } 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; + max_block_size = 1; } else { sfp->i2c = NULL; return -EINVAL; } + sfp->i2c_max_block_size = max_block_size; return 0; }
base-commit: c303e8b86d9dbd6868f5216272973292f7f3b7f1 -- 2.48.1