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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Maxime Chevallier Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, =?UTF-8?q?Bj=C3=B8rn=20Mork?= , Jonas Jelonek Subject: [PATCH net-next v6 2/2] net: sfp: extend SMBus support Date: Tue, 5 May 2026 20:06:47 +0000 Message-ID: <20260505200647.1125311-3-jelonek.jonas@gmail.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260505200647.1125311-1-jelonek.jonas@gmail.com> References: <20260505200647.1125311-1-jelonek.jonas@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Commit 7662abf4db94 ("net: phy: sfp: Add support for SMBus module access") added SMBus access for SFP modules, but limited it to single-byte transfers. As a side effect, hwmon is disabled (16-bit reads cannot be guaranteed atomic) and a warning is printed. Many SMBus-only I2C controllers in the wild support more than just byte access, and SFP cages are often wired to such controllers rather than to a full-featured I2C controller -- e.g. the SMBus controllers in the Realtek longan and mango SoCs, which advertise word access and I2C block reads. Today, they cannot drive an SFP at all without falling back to the byte-only path. Extend sfp_smbus_read()/sfp_smbus_write() so that, in addition to the existing byte access, they also use SMBus word access and SMBus I2C block access whenever the adapter advertises them. Both directions are handled in a single read and a single write helper that pick the largest supported transfer per chunk and fall back as needed. I2C-block is preferred unconditionally when available: the protocol carries any length 1..32, so it can serve every chunk -- including the 1- and 2-byte tails -- without help from word or byte access. Note that this requires I2C_FUNC_SMBUS_I2C_BLOCK, which reads a caller-specified number of bytes. This deviates from the official SMBus Block Read (length is supplied by the slave) but is widely supported by Linux I2C controllers/drivers. Capability matrix this implementation supports: - BYTE only: works (unchanged behaviour); 1-byte xfers, hwmon disabled. - BYTE + WORD: word for >=2-byte chunks, byte for trailing odd byte. - I2C_BLOCK present (with or without BYTE/WORD): block as the universal transport for every chunk. - WORD only (no BYTE/BLOCK): accepted with WARN_ONCE. Even-length transfers work; odd-length transfers (e.g. the 3-byte cotsworks fixup write) hit the BYTE branch which the adapter does not implement, so the xfer returns an error and the operation is aborted. No mainline I2C driver was found to advertise WORD without BYTE; the warning lets us learn about it if it ever shows up. Adapters with asymmetric R/W capabilities (e.g. only READ_I2C_BLOCK but not WRITE_I2C_BLOCK) remain functionally correct -- the per-iteration fallback uses the direction-specific bits -- but the shared i2c_max_block_size is sized by the all-bits-set check, so a transfer in the better-supported direction is not upgraded. None of the mainline I2C bus drivers surveyed during review advertise such asymmetry; promoting i2c_max_block_size to per-direction sizes can be revisited if needed. Signed-off-by: Jonas Jelonek --- drivers/net/phy/sfp.c | 134 +++++++++++++++++++++++++++++++++--------- 1 file changed, 107 insertions(+), 27 deletions(-) diff --git a/drivers/net/phy/sfp.c b/drivers/net/phy/sfp.c index e58e29a1e8d2..8ad650cbe862 100644 --- a/drivers/net/phy/sfp.c +++ b/drivers/net/phy/sfp.c @@ -14,6 +14,7 @@ #include #include #include +#include #include #include "sfp.h" @@ -756,50 +757,110 @@ 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_smbus_byte_read(struct sfp *sfp, bool a2, u8 dev_addr, - void *buf, size_t len) +static int sfp_smbus_read(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; + size_t this_len, transferred; + u32 functionality; 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; + functionality = i2c_get_functionality(sfp->i2c); - *data = smbus_data.byte; + while (len) { + this_len = min(len, sfp->i2c_max_block_size); + + if (functionality & I2C_FUNC_SMBUS_READ_I2C_BLOCK) { + 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); + transferred = this_len; + } else if (this_len >= 2 && + (functionality & I2C_FUNC_SMBUS_READ_WORD_DATA)) { + ret = i2c_smbus_xfer(sfp->i2c, bus_addr, 0, + I2C_SMBUS_READ, dev_addr, + I2C_SMBUS_WORD_DATA, &smbus_data); + if (ret < 0) + return ret; + + put_unaligned_le16(smbus_data.word, data); + transferred = 2; + } else { + 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; + transferred = 1; + } - len--; - data++; - dev_addr++; + data += transferred; + len -= transferred; + dev_addr += transferred; } return data - (u8 *)buf; } -static int sfp_smbus_byte_write(struct sfp *sfp, bool a2, u8 dev_addr, - void *buf, size_t len) +static int sfp_smbus_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; + size_t this_len, transferred; + u32 functionality; u8 *data = buf; int ret; + functionality = i2c_get_functionality(sfp->i2c); + 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; + this_len = min(len, sfp->i2c_max_block_size); + + if (functionality & I2C_FUNC_SMBUS_WRITE_I2C_BLOCK) { + 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 < 0) + return ret; + + transferred = this_len; + } else if (this_len >= 2 && + (functionality & I2C_FUNC_SMBUS_WRITE_WORD_DATA)) { + smbus_data.word = get_unaligned_le16(data); + ret = i2c_smbus_xfer(sfp->i2c, bus_addr, 0, + I2C_SMBUS_WRITE, dev_addr, + I2C_SMBUS_WORD_DATA, &smbus_data); + if (ret < 0) + return ret; + + transferred = 2; + } else { + 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 < 0) + return ret; + + transferred = 1; + } - len--; - data++; - dev_addr++; + data += transferred; + len -= transferred; + dev_addr += transferred; } return data - (u8 *)buf; @@ -815,10 +876,29 @@ static int sfp_i2c_configure(struct sfp *sfp, struct i2c_adapter *i2c) sfp->read = sfp_i2c_read; sfp->write = sfp_i2c_write; 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; - max_block_size = 1; + } else if (i2c_check_functionality(i2c, I2C_FUNC_SMBUS_BYTE_DATA) || + i2c_check_functionality(i2c, I2C_FUNC_SMBUS_I2C_BLOCK)) { + /* I2C-block carries any length 1..32, byte serves the + * 1-byte tail when block is absent: either alone is a + * complete transport. + */ + sfp->read = sfp_smbus_read; + sfp->write = sfp_smbus_write; + + if (i2c_check_functionality(i2c, I2C_FUNC_SMBUS_I2C_BLOCK)) + max_block_size = SFP_EEPROM_BLOCK_SIZE; + else if (i2c_check_functionality(i2c, I2C_FUNC_SMBUS_WORD_DATA)) + max_block_size = 2; + else + max_block_size = 1; + } else if (i2c_check_functionality(i2c, I2C_FUNC_SMBUS_WORD_DATA)) { + /* Word-only: even-length xfers work; odd-length xfers + * will error out at i2c_smbus_xfer(). + */ + WARN_ONCE(1, "sfp: SMBus word-only adapter; odd-length transfers will fail\n"); + sfp->read = sfp_smbus_read; + sfp->write = sfp_smbus_write; + max_block_size = 2; } else { sfp->i2c = NULL; return -EINVAL; -- 2.51.0