netdev - Re: Aquantia PHY in OCSGMII mode?

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20250828092859.vvejz6xrarisbl2w@skbuf>
Date: Thu, 28 Aug 2025 12:28:59 +0300
From: Vladimir Oltean <vladimir.oltean@....com>
To: Alexander Wilhelm <alexander.wilhelm@...termo.com>,
	"Russell King (Oracle)" <linux@...linux.org.uk>
Cc: Andrew Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Aquantia PHY in OCSGMII mode?

On Wed, Aug 27, 2025 at 10:13:59AM +0100, Russell King (Oracle) wrote:
> On Wed, Aug 27, 2025 at 11:03:42AM +0200, Alexander Wilhelm wrote:
> > I asked the hardware engineer again. The point is that the MAC does not set
> > SGMII for 100M. It still uses 2500base-x but with 10x paket repetition.
> 
> No one uses symbol repetition when in 2500base-x mode. Nothing supports
> it. Every device datasheet I've read states clearly that symbol
> repetition is unsupported when operating at 2.5Gbps.
> 
> Also think about what this means. If the link is operating at 2.5Gbps
> with a 10x symbol repetition, that means the link would be passing
> 250Mbps. That's not compatible with _anything_.

FWIW, claim 5 of this active Cisco patent suggests dividing frames into
2 segments, replicating symbols from the first segment twice and symbols
from the second segment three times.
https://patents.google.com/patent/US7356047B1/en

I'm completely unaware of any implementations of this either, though.

To remain on topic, I don't see how the hardware engineer's claim can be
true. The PCS symbol replication is done through the IF_MODE_SPEED
field, which lynx_pcs_link_up_2500basex() sets to SGMII_SPEED_2500 (same
as SGMII_SPEED_1000, i.e. no replication). You can confirm that the
IF_MODE register has the expected value by putting a print.