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SubjectRe: [PATCH net-next] net: phy: sfp: handle cases where neither BR,min nor BR,max is given
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On May 4, 2018 8:21:03 AM PDT, Antoine Tenart <antoine.tenart@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.tenart@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!

--
Florian

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