On Sat, May 05, 2018 at 01:35:34PM -0700, Florian Fainelli wrote: > On May 4, 2018 8:21:03 AM PDT, Antoine Tenart <antoine.ten...@bootlin.com> > wrote: > >When computing the bitrate using values read from an SFP module EEPROM, > >we use the nominal BR plus BR,min and BR,max to determine the > >boundaries. But in some cases BR,min and BR,max aren't provided, which > >led the SFP code to end up having the nominal value for both the > >minimum > >and maximum bitrate values. When using a passive cable, the nominal > >value should be used as the maximum one, and there is no minimum one > >so we should use 0. > > > >Signed-off-by: Antoine Tenart <antoine.ten...@bootlin.com> > >--- > > > >Hi Russell, > > > >I'm not completely sure about this patch as this case is not really > >specified in the specification. But the issue is there, and I've > >discuss > >this with others. It seemed logical (at least to us :)) to use the > >BR,nominal values as br_max and 0 as br_min when using a passive cable > >which only provides BR,nominal as this would be the highest rate at > >which the cable could work. And because it's passive, there should be > >no > >issues using it at a lower rate. > > > >I've tested this with one passive cable which only reports its > >BR,nominal (which was 10300) while it could be used when using > >1000baseX > >or 2500baseX modes. > > Which SFP modules (vendor and model) exposed this out of curiosity? > Russell and I already saw the Cotsworks modules having so e issues > with checksums, so building a table of quirks would help. Thanks!
I think this is just manufacturers being lazy with their EEPROM contents - looking around, most passive cables are specified to be "up to" some figure, and that's definitely what's specified by the SFP+ specification by way of the high-pass pole requirement of the coupling capacitors. -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 8.8Mbps down 630kbps up According to speedtest.net: 8.21Mbps down 510kbps up
