netdev - Re: [PATCH net] net: sfp: initialize sfp->i2c_block

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Date:   Wed, 5 Apr 2023 23:41:16 +0300
From:   Ivan Bornyakov <i.bornyakov@...rotek.ru>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     netdev@...r.kernel.org, linux@...linux.org.uk,
        hkallweit1@...il.com, davem@...emloft.net, edumazet@...gle.com,
        kuba@...nel.org, pabeni@...hat.com, linux-kernel@...r.kernel.org,
        system@...rotek.ru, stable@...r.kernel.org
Subject: Re: [PATCH net] net: sfp: initialize sfp->i2c_block_size at sfp
 allocation

On Wed, Apr 05, 2023 at 09:35:31PM +0200, Andrew Lunn wrote:
> On Wed, Apr 05, 2023 at 06:39:00PM +0300, Ivan Bornyakov wrote:
> > sfp->i2c_block_size is initialized at SFP module insertion in
> > sfp_sm_mod_probe(). Because of that, if SFP module was not inserted
> > since boot, ethtool -m leads to zero-length I2C read attempt.
> > 
> >   # ethtool -m xge0
> >   i2c i2c-3: adapter quirk: no zero length (addr 0x0050, size 0, read)
> >   Cannot get Module EEPROM data: Operation not supported
> 
> Do i understand you correct in that this is when the SFP cage has
> always been empty? The I2C transaction is going to fail whatever the
> length is.
> 

Yes, SFP cage is empty, I2C transaction will fail anyways, but not all
I2C controllers are happy about zero-length reads.

> > If SFP module was plugged then removed at least once,
> > sfp->i2c_block_size will be initialized and ethtool -m will fail with
> > different error
> > 
> >   # ethtool -m xge0
> >   Cannot get Module EEPROM data: Remote I/O error
> 
> So again, the SFP cage is empty?
> 
> I wonder if a better fix is to use
> 
> sfp->state & SFP_F_PRESENT
> 
> in sfp_module_eeprom() and sfp_module_eeprom_by_page() and don't even
> do the I2C read if there is no module in the cage?
> 

This is also worthy addition to sfp.c, but IMHO sfp->i2c_block_size
initialization still need to be fixed since

  $ grep -c "sfp_read(" drivers/net/phy/sfp.c
  31

and I can't vouch all of them are possible only after SFP module
insertion. Also for future proof reason.