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Message-ID: <4628df96-5ad7-411b-9b9d-4084cb5da87a@gmail.com>
Date: Mon, 5 Jan 2026 16:49:51 +0100
From: Jonas Jelonek <jelonek.jonas@...il.com>
To: Russell King <linux@...linux.org.uk>, Andrew Lunn <andrew@...n.ch>,
Heiner Kallweit <hkallweit1@...il.com>,
"David S . Miller" <davem@...emloft.net>, Eric Dumazet
<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
Bjørn Mork <bjorn@...k.no>,
Maxime Chevallier <maxime.chevallier@...tlin.com>
Subject: Re: [PATCH v2] net: sfp: add SMBus I2C block support
Sorry for the noise, messed that version up.
Will send a v3 quickly.
Best regards,
Jonas Jelonek
On 05.01.26 16:46, Jonas Jelonek wrote:
> 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@...il.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/
> ---
> 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
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