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

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Date:   Tue, 12 Jan 2021 21:53:13 +0100
From:   Marek Behún <kabel@...nel.org>
To:     Andrew Lunn <andrew@...n.ch>
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

On Tue, 12 Jan 2021 21:43:29 +0100
Andrew Lunn <andrew@...n.ch> wrote:

> > +/* 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?

I forgot about the first comment. I will rewrite it and send again.

> 
> > +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

THX.

> 
> > +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.

C22 is not supported by this protocol. A few line above there is
  if (!(reg & MII_ADDR_C45))
    return -EOPNOTSUPP;

> 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

OK then, I will remove this.

Thanks, Andrew.