Re: [PATCH net-next v1] net: phy: sfp: detect presence via I2C when no MOD_DEF0 GPIO

[Andrew Lunn]

> > Did you try a 0 byte read? That is what tools like i2cdetect use.
> 
> I can't on this board: the cage I2C master is the RTL9303's SMBus
> controller, which advertises only I2C_FUNC_SMBUS_BYTE_DATA -- no
> I2C_FUNC_I2C and, notably, no SMBus Quick Command

O.K. So the board design is broken. To properly use an SFP you need
two byte reads :-(

Anyway, i was thinking 0 byte might be more reliable. We know SFPs get
all sorts of things wrong, even simple things like reading a word. Can
they get reading 0 bytes wrong? I suppose it is not a typical use
case, so probably yes :-)

So lets stick to 1-byte reads.

      Andrew