netdev - Re: [PATCH net-next 2/6] net: txgbe: Implement I2C bus master driver

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Date:   Mon, 3 Apr 2023 14:52:59 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Jiawen Wu <jiawenwu@...stnetic.com>
Cc:     netdev@...r.kernel.org, linux@...linux.org.uk,
        mengyuanlou@...-swift.com
Subject: Re: [PATCH net-next 2/6] net: txgbe: Implement I2C bus master driver

On Mon, Apr 03, 2023 at 02:45:24PM +0800, Jiawen Wu wrote:
> I2C bus is integrated in Wangxun 10Gb ethernet chip. Implement I2C bus
> driver to receive I2C messages.

Please Cc: the i2c mailing list for comments. They know more about I2C
than the netdev people.

Is the I2C bus master your own IP, or have you licensed a core? Or
using the open cores i2C bus master? I just want to make sure there is
not already a linux driver for this.
 
> +static void txgbe_i2c_start(struct wx *wx, u16 dev_addr)
> +{
> +	wr32(wx, TXGBE_I2C_ENABLE, 0);
> +
> +	wr32(wx, TXGBE_I2C_CON,
> +	     (TXGBE_I2C_CON_MASTER_MODE |
> +	      TXGBE_I2C_CON_SPEED(1) |
> +	      TXGBE_I2C_CON_RESTART_EN |
> +	      TXGBE_I2C_CON_SLAVE_DISABLE));
> +	/* Default addr is 0xA0 ,bit 0 is configure for read/write! */

A generic I2C bus master should not care about that address is being
read/write. For the SFP use case, 0xa0 will be used most of the time,
plus 0xa2 for diagnostics. But when the SFP contains a copper PHY,
other addresses will be used as well.

> +static int txgbe_i2c_xfer(struct i2c_adapter *i2c_adap,
> +			  struct i2c_msg *msg, int num_msgs)
> +{
> +	struct wx *wx = i2c_get_adapdata(i2c_adap);
> +	u8 *dev_addr = msg[0].buf;
> +	bool read = false;
> +	int i, ret;
> +	u8 *buf;
> +	u16 len;
> +
> +	txgbe_i2c_start(wx, msg[0].addr);
> +
> +	for (i = 0; i < num_msgs; i++) {
> +		if (msg[i].flags & I2C_M_RD) {
> +			read = true;
> +			len = msg[i].len;
> +			buf = msg[i].buf;
> +		}
> +	}
> +
> +	if (!read) {
> +		wx_err(wx, "I2C write not supported\n");
> +		return num_msgs;
> +	}

Write is not supported at all? Is this a hardware limitation?  I think
-EOPNOTSUPP is required here, and you need to ensure the code using
the I2C bus master has quirks to not try to write.

> +#define TXGBE_I2C_SLAVE_ADDR                    (0xA0 >> 1)
> +#define TXGBE_I2C_EEPROM_DEV_ADDR               0xA0

These two do not appear to be used? I guess you took your hard coded
SFP i2c bus master and generalised it? Please clean up dead code like
this.

	Andrew