linux-kernel - Re: [PATCH net] net: mvpp2: Enable autoneg bypass for 1000BaseX/2500BaseX ports

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Message-ID: <20200528220420.GY1551@shell.armlinux.org.uk>
Date:   Thu, 28 May 2020 23:04:20 +0100
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Thomas Bogendoerfer <tbogendoerfer@...e.de>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: mvpp2: Enable autoneg bypass for
 1000BaseX/2500BaseX ports

On Thu, May 28, 2020 at 08:43:12PM +0200, Thomas Bogendoerfer wrote:
> On Thu, 28 May 2020 15:48:05 +0100
> Russell King - ARM Linux admin <linux@...linux.org.uk> wrote:
> 
> > On Thu, May 28, 2020 at 04:33:35PM +0200, Thomas Bogendoerfer wrote:
> > > below is the dts part for the two network interfaces. The switch to
> > > the outside has two ports, which correlate to the two internal ports.
> > > And the switch propagates the link state of the external ports to
> > > the internal ports.
> > 
> > Okay, so this DTS hasn't been reviewed...
> 
> that's from our partner, I'm just using it. Stripping it down isn't
> the point for my now.
> 
> > This isn't correct - you are requesting that in-band status is used
> > (i.o.w. the in-band control word, see commit 4cba5c210365), but your
> > bug report wants to enable AN bypass because there is no in-band
> > control word.  This seems to be rather contradictory.
> > 
> > May I suggest you use a fixed-link here, which will not have any
> 
> afaik fixed-link will always be up, and we want to have the link state
> from the switch external ports.
> 
> > inband status, as there is no in-band control word being sent by
> > the switch?  That is also the conventional way of handling switch
> > links.
> 
> again, we want to propagte the external link state inside to all
> the internal nodes. So this will not work anymore with fixed-link.

Can you explain this please?  Just as we think we understand what's
going on here, you throw in a new comment that makes us confused.

You said previously that the mvpp2 was connected to a switch, which
makes us think that you've got some DSA-like setup going on here.
Does your switch drop its serdes link when all the external links
(presumably the 10G SFP+ cages) fail?

Both Andrew and myself wish to have a complete picture before we
move forward with this.

Thanks.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTC for 0.8m (est. 1762m) line in suburbia: sync at 13.1Mbps down 424kbps up