On Tue, 20 Oct 2020 18:00:39 +0200
Andrew Lunn [off-list ref] wrote:

quoted

This extends the mdio-i2c driver so that when SFP PHY address 17 is used
(which in mdio-i2c terms corresponds to I2C address 0x51), then this
different protocol is used for MDIO access.  

Hi Marek

I don't see that being very scalable. What happens when the next SFP
comes along which has a different protocol at address 0x51. Since you
can identify the SFP via the EEPROM information, i would prefer you
explicitly tell it to use the rollball protocol when instantiating the
MDIO bus.

At first I proposed a separate mdio bus driver for RollBall SFPs.
But Russell suggested doing this instead, saying that in the future
this can be changed.

quoted

  * I2C bus addresses 0x50 and 0x51 are normally an EEPROM, which is
  * specified to be present in SFP modules.  These correspond with PHY
- * addresses 16 and 17.  Disallow access to these "phy" addresses.
+ * addresses 16 and 17.  Disallow access to 0x50 "phy" address.
+ * Use RollBall protocol when accessing via the 0x51 address.
  */
 static bool i2c_mii_valid_phy_id(int phy_id)
 {
-	return phy_id != 0x10 && phy_id != 0x11;
+	return phy_id != 0x10;
+}  

I'm not sure that is safe. It means that we will scan address 0x11 to
see if there is a PHY there. And if the SFP does have diagnostics
registers, that might be enough that phylib thinks there is a PHY
there.

I think you only need to allow access to 0x11 if rollball protocol has
been enabled.

I can do that...

     Andrew