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

[Russell King - ARM Linux]

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.
> 
> Hi Antoine, Russell
> 
> 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?

While we can support forcing the speed/duplex through ethtool, there
is no obvious facility via ethtool to set the protocol currently (eg,
SGMII vs 1000base-X).  There is, however, the possibility to use the
advertise mask to determine which mode we should be using, but that's
awkward to deal with via ethtool as ethtool wants a hex mask, which
really isn't user friendly.

The protocol matters - for example, a copper SFP module will typically
want to use SGMII, and if it encounters 1000base-X on the other side,
the PHY won't pass data because it will believe that the link to the
MAC is down.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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