netdev - Re: [PATCH net-next 1/5] net: phy: mdio-i2c: support I2C MDIO protocol for RollBall SFP modules

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Message-ID: <20201029124141.GR1551@shell.armlinux.org.uk>
Date:   Thu, 29 Oct 2020 12:41:41 +0000
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Marek Behún <kabel@...nel.org>
Cc:     netdev@...r.kernel.org, davem@...emloft.net,
        Andrew Lunn <andrew@...n.ch>
Subject: Re: [PATCH net-next 1/5] net: phy: mdio-i2c: support I2C MDIO
 protocol for RollBall SFP modules

On Wed, Oct 28, 2020 at 11:14:23PM +0100, Marek Behún wrote:
> Some multigig SFPs from RollBall and Hilink do not expose functional
> MDIO access to the internal PHY of the SFP via I2C address 0x56
> (although there seems to be read-only clause 22 access on this address).
> 
> Instead these SFPs PHY can be accessed via I2C via the SFP Enhanced
> Digital Diagnostic Interface - I2C address 0x51.
> 
> This extends the mdio-i2c driver to support this protocol by adding a
> special parameter to mdio_i2c_alloc function via which this RollBall
> protocol can be selected.
> 
> Signed-off-by: Marek Behún <kabel@...nel.org>
> Cc: Andrew Lunn <andrew@...n.ch>
> Cc: Russell King <rmk+kernel@...linux.org.uk>

I think this is probably a better way forward, and I suspect we're going
to see more of this stuff. I wonder, however, whether the configuration
should be done here too (selecting page 1). Also, shouldn't we ensure
that we are on page 1 before attempting any access?

It would be good to pass this through checkpatch - I notice some lines
seem to be over the 80 character limit now.

A few comments below...

> +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 buf0[2], *res;
> +	int i, ret;
> +
> +	buf0[0] = ROLLBALL_CMD_ADDR;
> +
> +	msgs[0].addr = bus_addr;
> +	msgs[0].flags = 0;
> +	msgs[0].len = 1;
> +	msgs[0].buf = &buf0[0];
> +
> +	res = buf ? buf : &buf0[1];
> +
> +	msgs[1].addr = bus_addr;
> +	msgs[1].flags = I2C_M_RD;
> +	msgs[1].len = buf ? len : 1;
> +	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;
> +
> +	ret = i2c_rollball_mii_cmd(bus, bus_addr, ROLLBALL_CMD_READ, buf, sizeof(buf));
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = i2c_rollball_mii_poll(bus, bus_addr, res, sizeof(res));
> +	if (ret == -ETIMEDOUT)
> +		return 0xffff;
> +	else if (ret < 0)
> +		return ret;
> +
> +	val = res[4];
> +	val <<= 8;
> +	val |= res[5];

Was there something wrong with:

	val = res[4] << 8 | res[5];

here?

> +struct mii_bus *mdio_i2c_alloc(struct device *parent, struct i2c_adapter *i2c,
> +			       enum mdio_i2c_type type)

Maybe call this "protocol" rather than "type" ?

> +enum mdio_i2c_type {
> +	MDIO_I2C_DEFAULT,
> +	MDIO_I2C_ROLLBALL,
> +};
> +
> +struct mii_bus *mdio_i2c_alloc(struct device *parent, struct i2c_adapter *i2c,
> +			       enum mdio_i2c_type type);

Same here (protocol vs type).

Otherwise, I don't see much else wrong.

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