netdev - Re: [PATCH net-next v4 1/4] net: phy: mdio-i2c: support I2C MDIO protocol for RollBall SFP modules

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Message-ID: <X/4J8cB1ITZmesN5@lunn.ch>
Date:   Tue, 12 Jan 2021 21:43:29 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Marek Behún <kabel@...nel.org>
Cc:     netdev@...r.kernel.org, Russell King <rmk+kernel@...linux.org.uk>,
        Jakub Kicinski <kuba@...nel.org>, davem@...emloft.net,
        pali@...nel.org
Subject: Re: [PATCH net-next v4 1/4] net: phy: mdio-i2c: support I2C MDIO
 protocol for RollBall SFP modules

> +/* RollBall SFPs do not access internal PHY via I2C address 0x56, but
> + * instead via address 0x51, when SFP page is set to 0x03 and password to
> + * 0xffffffff.
> + * Since current SFP code does not modify SFP_PAGE, we set it to 0x03 only at
> + * bus creation time, and expect it to remain set to 0x03 throughout the
> + * lifetime of the module plugged into the system. If the SFP code starts
> + * modifying SFP_PAGE in the future, this code will need to change.

...

> +/* In order to not interfere with other SFP code (which possibly may manipulate
> + * SFP_PAGE), for every transfer we do this:
> + *   1. lock the bus
> + *   2. save content of SFP_PAGE
> + *   3. set SFP_PAGE to 3
> + *   4. do the transfer
> + *   5. restore original SFP_PAGE
> + *   6. unlock the bus

These two comments seem to contradict each other?

> +static int i2c_rollball_mii_poll(struct mii_bus *bus, int bus_addr, u8 *buf,
> +				 size_t len)
> +{
> +	struct i2c_adapter *i2c = bus->priv;
> +	struct i2c_msg msgs[2];
> +	u8 cmd_addr, tmp, *res;
> +	int i, ret;
> +
> +	cmd_addr = ROLLBALL_CMD_ADDR;
> +
> +	res = buf ? buf : &tmp;
> +	len = buf ? len : 1;
> +
> +	msgs[0].addr = bus_addr;
> +	msgs[0].flags = 0;
> +	msgs[0].len = 1;
> +	msgs[0].buf = &cmd_addr;
> +
> +	msgs[1].addr = bus_addr;
> +	msgs[1].flags = I2C_M_RD;
> +	msgs[1].len = len;
> +	msgs[1].buf = res;
> +
> +	/* By experiment it takes up to 70 ms to access a register for these
> +	 * SFPs. Sleep 20ms between iteratios and try 10 times.
> +	 */

iterations

> +static int i2c_mii_read_rollball(struct mii_bus *bus, int phy_id, int reg)
> +{
> +	u8 buf[4], res[6];
> +	int bus_addr, ret;
> +	u16 val;
> +
> +	if (!(reg & MII_ADDR_C45))
> +		return -EOPNOTSUPP;
> +
> +	bus_addr = i2c_mii_phy_addr(phy_id);
> +	if (bus_addr != ROLLBALL_PHY_I2C_ADDR)
> +		return 0xffff;
> +
> +	buf[0] = ROLLBALL_DATA_ADDR;
> +	buf[1] = (reg >> 16) & 0x1f;
> +	buf[2] = (reg >> 8) & 0xff;
> +	buf[3] = reg & 0xff;

This looks odd. There are only 32 registers for C22 transactions, so
it fits in one byte. You can set buf[1] and buf[2] to zero.

C45 transactions allow for 65536 registers, and has the devtype field,
so would need 3 bytes. Which suggests that C45 might actually be
supported? At least by the protocol, if not the device.

> +	dev_dbg(&bus->dev, "read reg %02x:%04x = %04x\n", (reg >> 16) & 0x1f,
> +		reg & 0xffff, val);

There is a tracepoint that allows access to this information, so you
can probably remove this.

    Andrew