Re: [PATCH v2] net: sfp: add SMBus I2C block support

[Jonas Jelonek <jelonek.jonas@gmail.com>]

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@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/
> ---
>  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