linux-kernel - Re: [PATCH net] net: sfp: initialize sfp->i2c_block

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Date:   Wed, 5 Apr 2023 21:35:31 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Ivan Bornyakov <i.bornyakov@...rotek.ru>
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 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.

> 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?

   Andrew