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

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Message-ID: <20180517125648.GM32746@kwain>
Date:   Thu, 17 May 2018 14:56:48 +0200
From:   Antoine Tenart <antoine.tenart@...tlin.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Antoine Tenart <antoine.tenart@...tlin.com>, 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

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.

So the question is, do we want to enable partially working SFP cages
(ie. probably working with only a subset of SFP modules)?

Thanks!
Antoine

-- 
Antoine Ténart, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com