Re: [PATCH net-next v2 1/2] net: phy: sfp: Add support for SMBus module access

[Maxime Chevallier]

On Tue, 25 Feb 2025 18:04:29 +0000
"Russell King (Oracle)" <linux@xxxxxxxxxxxxxxx> wrote:

> On Tue, Feb 25, 2025 at 12:20:39PM +0100, Maxime Chevallier wrote:
> > The SFP module's eeprom and internals are accessible through an i2c bus.
> > However, all the i2c transfers that are performed are SMBus-style
> > transfers for read and write operations.  
> 
> Note that there are SFPs that fail if you access them by byte - the
> 3FE46541AA locks the bus if you byte access the emulated EEPROM at
> 0x50, address 0x51. This is documented in sfp_sm_mod_probe().
> 
> So there's a very real reason for adding the warning - this module
> will not work!

That's indeed pretty serious and since we can't even read the
eeprom, there's not even a chance to have, say, a list of modules that
will break with 1-byte io. So indeed the warning is needed...

Thanks

Maxime