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

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Message-ID: <aVvjyWzKuczNf3lt@shell.armlinux.org.uk>
Date: Mon, 5 Jan 2026 16:16:09 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Jonas Jelonek <jelonek.jonas@...il.com>
Cc: 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>,
	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

On Mon, Jan 05, 2026 at 03:46:53PM +0000, Jonas Jelonek wrote:
> @@ -765,26 +794,70 @@ static int sfp_smbus_byte_write(struct sfp *sfp, bool a2, u8 dev_addr,
>  		dev_addr++;
>  	}
>  
> +	return data - (u8 *)buf;

A separate fix is being submitted for this.

> +}
> +
> +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;

This is wrong. As already said, the I2C accessors return the number of
bytes successfully transferred. Zero means no bytes were transferred,
which is an error.

All callers to sfp_write() validate that the expected number of bytes
were written. Thus, returning zero will cause failures.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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