linux-kernel - Re: [PATCH net-next v3 0/5] TSN auto negotiation between 1G and 2.5G

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

Date:   Thu, 21 Sep 2023 15:09:05 +0100
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Choong Yong Liang <yong.liang.choong@...ux.intel.com>,
        Rajneesh Bhardwaj <irenic.rajneesh@...il.com>,
        David E Box <david.e.box@...ux.intel.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Mark Gross <markgross@...nel.org>,
        Jose Abreu <Jose.Abreu@...opsys.com>,
        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>,
        Marek Behún <kabel@...nel.org>,
        Jean Delvare <jdelvare@...e.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Jose Abreu <joabreu@...opsys.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Richard Cochran <richardcochran@...il.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Wong Vee Khee <veekhee@...le.com>,
        Jon Hunter <jonathanh@...dia.com>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Revanth Kumar Uppala <ruppala@...dia.com>,
        Shenwei Wang <shenwei.wang@....com>,
        Andrey Konovalov <andrey.konovalov@...aro.org>,
        Jochen Henneberg <jh@...neberg-systemdesign.com>,
        David E Box <david.e.box@...el.com>,
        Andrew Halaney <ahalaney@...hat.com>,
        Simon Horman <simon.horman@...igine.com>,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org,
        platform-driver-x86@...r.kernel.org, linux-hwmon@...r.kernel.org,
        bpf@...r.kernel.org, Voon Wei Feng <weifeng.voon@...el.com>,
        Tan Tee Min <tee.min.tan@...ux.intel.com>,
        Michael Sit Wei Hong <michael.wei.hong.sit@...el.com>,
        Lai Peter Jun Ann <jun.ann.lai@...el.com>
Subject: Re: [PATCH net-next v3 0/5] TSN auto negotiation between 1G and 2.5G

On Thu, Sep 21, 2023 at 03:14:59PM +0200, Andrew Lunn wrote:
> > Auto-negotiation between 10, 100, 1000Mbps will use
> > in-band auto negotiation. Auto-negotiation between 10/100/1000Mbps and
> > 2.5Gbps will work as the following proposed flow, the stmmac driver reads
> > the PHY link status registers then identifies the negotiated speed.
> 
> I don't think you replied to my comment.
> 
> in-band is just an optimisation. It in theory allows you to avoid a
> software path, the PHY driver talking to the MAC driver about the PHY
> status. As an optimisation, it is optional. Linux has the software
> path and the MAC driver you are using basically has it implemented.

Sorry Andrew, I have to disagree. It isn't always optional - there are
PHYs out there where they won't pass data until the in-band exchange
has completed. If you try to operate out-of-band without the PHY being
told that is the case, and program the MAC/PCS end not to respond to
the in-band frames from the PHY, the PHY will report link up as normal
(since it reports the media side), but no data will flow because the
MAC facing side of the PHY hasn't completed.

The only exception are PHYs that default to in-band but have an inband
bypass mode also enabled to cover the case where the MAC/PCS doesn't
respond to the inband messages.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!