Message-ID: <5AAC2BA1.5854.31008546@Frantisek.Rysanek.post.cz>
Date:   Fri, 16 Mar 2018 21:40:01 +0100
From:   "Frantisek Rysanek" <Frantisek.Rysanek@...t.cz>
To:     Andrew Lunn <andrew@...n.ch>
CC:     netdev@...r.kernel.org
Subject: Re: HW question: i210 vs. BCM5461S over SGMII: no response from PHY to MDIO requests?

On 16 Mar 2018 at 19:42, Andrew Lunn wrote:
> Hi Frantisek
> 
> This seems a bit odd. The SFP cage only has i2c, not MDIO. It is
> possible to carry MDIO over i2c, which is what is done when the SFP
> module is copper, not fibre. But you are doing 100Base-FX, so fibre.
> 
> The BCM5461 is a copper PHY. There are some PHYs which are designed to
> act as translators. You can feed SERDES in one side, and get SGMII out
> the other side, for example. Such PHYs can be used between a MAC and
> an SFP socket. But from what i can find online about the BCM5461, it
> does not have this capability.
> 
> Can you tell us the exact make/model of the DeLock card and the SFP
> modules.
> 
> 	Andrew
>

Hello Andrew,

thanks for your polite response.

The DeLock board is this beauty:
http://www.delock.de/produkte/G_89481/merkmale.html?setLanguage=en
DeLock techsupport were so kind as to provide me with a schematic 
snippet, showing the wiring of the i210 fiber SKU's dedicated 
I2C/MDIO pins to the SFP socket's standard I2C pins. There are 
pull-up resistors on the board for SDA/SCL. Nothing outright custom 
here - more likely close to some Intel reference design. The board 
works just fine.

Interesting - I've noticed before that the sparse Broadcom data brief
for the BCM5461S doesn't cotain a word about 100Base-FX.
This might be a good question to the SFP vendor's techsupport :-)
The 54616S datasheet does mention 100Base-FX, but I have no reason to 
believe that my SFP contains that chip.

It was mostly my naive assumption that the BCM5461S would speak 
MDIO/MDC via the SFP slot's I2C lines :-) The i210 pinout allows for 
that and the BCM5461S doesn't seem to have I2C for management. It 
does have MDIO and MDC. I've tried the "SGMII with i2c management" 
option too - as I said the SFP seems to be responding, but the 
response is some junk. Not corresponding to what the Intel driver 
expects.

As for the SFP's... 

The one that I actually bought as shiny new and speaking SGMII, and 
that contains a chip labeled 5461SA, is sold as Huwei-compatible. 
I do not know what that means at pinout level and protocol level :-)  
"got it at e-bay" says it all. Yet, I have to say that I've been 
politely and firmly warned by the selling party that it's not gonna 
work in my Intel board. I bought it anyway, out of curiosity. So I'm 
not going to provide a link, unless I find something to praise on the 
product :-)
I cannot exclude the possibility that the SFP is a fake, despite 
being mechanically/visually a masterpiece.

The other SFP I got for free, with a comment that "it's some Chinese 
junk, supposedly SGMII compatible, but it hasn't ever worked for us 
in any hardware. Here you go, have it." And the chips inside are 
obscured between two PCB's = no idea what they are, unless I take
a hot air pen to it.

I'll probably take some macro photoes of the SFP internals
(on monday) and post them. Perhaps the set of chips may ring a bell 
with someone here :-)

For the moment, thanks for your attention.

Frank Rysanek

Customer support
FCC prumyslove systemy s.r.o.
Usti nad Labem
Czech Republic
+420 47 2774 173 (office)
+420 736 630 449 (mobile)
rysanek@...ps.cz

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