netdev - Re: [PATCH net-next] net: phy: sfp: handle cases where neither BR,min nor BR,max is given

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Date:   Sat, 05 May 2018 13:35:34 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Antoine Tenart <antoine.tenart@...tlin.com>, davem@...emloft.net,
        linux@...linux.org.uk
CC:     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] net: phy: sfp: handle cases where neither BR,min nor BR,max is given

On May 4, 2018 8:21:03 AM PDT, Antoine Tenart <antoine.tenart@...tlin.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.tenart@...tlin.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!

-- 
Florian