netdev - Re: [PATCH net-next 1/2] net: phy: sfp: make the i2c-bus property really optional

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Message-ID: <20180517130406.GH8547@lunn.ch>
Date:   Thu, 17 May 2018 15:04:06 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Antoine Tenart <antoine.tenart@...tlin.com>
Cc:     davem@...emloft.net, linux@...linux.org.uk, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, thomas.petazzoni@...tlin.com,
        maxime.chevallier@...tlin.com, gregory.clement@...tlin.com,
        miquel.raynal@...tlin.com, nadavh@...vell.com, stefanc@...vell.com,
        ymarkman@...vell.com, mw@...ihalf.com
Subject: Re: [PATCH net-next 1/2] net: phy: sfp: make the i2c-bus property
 really optional

On Thu, May 17, 2018 at 02:56:48PM +0200, Antoine Tenart wrote:
> Hi Andrew,
> 
> On Thu, May 17, 2018 at 02:41:28PM +0200, Andrew Lunn wrote:
> > On Thu, May 17, 2018 at 10:29:06AM +0200, Antoine Tenart wrote:
> > > The SFF,SFP documentation is clear about making all the DT properties,
> > > with the exception of the compatible, optional. In practice this is not
> > > the case and without an i2c-bus property provided the SFP code will
> > > throw NULL pointer exceptions.
> > > 
> > > This patch is an attempt to fix this.
> > 
> > How usable is an SFF/SFP module without access to the i2c EEPROM? I
> > guess this comes down to link speed. Can it be manually configured?
> >
> > I'm just wondering if we want to make this mandatory? Fail the probe
> > if it is not listed?
> 
> Yes, the other option would be to fail when probing a cage missing the
> i2c description. I'd say a passive module can work without the i2c
> EEPROM accessible as it does not need to be configured. I don't know
> what would happen with active ones.

Hi Antoine

I was thinking about how it reads the bit rate from the EEPROM. From
that it determines what mode the MAC could use, 1000-Base-X,
2500-Base-X, etc. Can you still configure this correctly via ethtool,
if you don't have the bitrate information?

   Andrew