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

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Date: Fri, 14 Jul 2023 06:26:14 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Feiyang Chen <chris.chenfeiyang@...il.com>
Cc: Feiyang Chen <chenfeiyang@...ngson.cn>, hkallweit1@...il.com,
	peppe.cavallaro@...com, alexandre.torgue@...s.st.com,
	joabreu@...opsys.com, chenhuacai@...ngson.cn, linux@...linux.org.uk,
	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.

When the line side speed changes, the PHY will first report link down
via the adjust_link callback in the MAC driver. Once the PHY has
determined the new speed, the adjust_link callback will be called
again with the new speed and pause parameters.

So what is actually going wrong?

   Andrew