netdev - Re: [RFC PATCH 10/10] net: stmmac: dwmac-loongson: Add GNET support

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Message-ID: <ZLELE5ysytsynpjr@shell.armlinux.org.uk>
Date: Fri, 14 Jul 2023 09:45:07 +0100
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Feiyang Chen <chris.chenfeiyang@...il.com>
Cc: Andrew Lunn <andrew@...n.ch>, Feiyang Chen <chenfeiyang@...ngson.cn>,
	hkallweit1@...il.com, peppe.cavallaro@...com,
	alexandre.torgue@...s.st.com, joabreu@...opsys.com,
	chenhuacai@...ngson.cn, dongbiao@...ngson.cn,
	loongson-kernel@...ts.loongnix.cn, netdev@...r.kernel.org,
	loongarch@...ts.linux.dev
Subject: Re: [RFC PATCH 10/10] net: stmmac: dwmac-loongson: Add GNET support

On Fri, Jul 14, 2023 at 10:24:37AM +0800, Feiyang Chen wrote:
> On Thu, Jul 13, 2023 at 12:07 PM Andrew Lunn <andrew@...n.ch> wrote:
> >
> > On Thu, Jul 13, 2023 at 10:49:38AM +0800, Feiyang Chen wrote:
> > > Add GNET support. Use the fix_mac_speed() callback to workaround
> > > issues with the Loongson PHY.
> >
> > What are the issues?
> >
> 
> Hi, Andrew,
> 
> There is an issue with the synchronization between the network card
> and the PHY. In the case of gigabit operation, if the PHY's speed
> changes, the network card's speed remains unaffected. Hence, it is
> necessary to initiate a re-negotiation process with the PHY to align
> the link speeds properly.

Please could you explain a bit more what happens when "the PHY's speed
changes". Are you suggesting that:

You have a connection where the media side has negotiated 1G speed.
The gigabit partner is disconnected, so the link goes down, and is then
replaced by a partner only capable of 100M. The link comes back up at
100M, but the network card continues trying to operate at 1G?

Thanks.

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