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

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Date: Mon, 17 Jul 2023 15:54:17 +0800
From: Feiyang Chen <chris.chenfeiyang@...il.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>, Andrew Lunn <andrew@...n.ch>
Cc: 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 4:45 PM Russell King (Oracle)
<linux@...linux.org.uk> wrote:
>
> 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?
>

Hi, Russell, Andrew,

This bug shows up in the following way: when the speed is set to 1000M,
PHY is set up correctly and its status is normal. However, the controller
and PHY don't work well together, causing the controller to fail in
establishing a gigabit connection, which leads to a network disruption.
So, we need to use this bit to check if the controller's status is correct
and reset PHY if necessary.

if (readl(ptr->ioaddr + MAC_CTRL_REG) & (1 << 15) /* PS */)

The troublesome issue is that we have to check this bit in stmmac.
As a result, we are forced to place phy_restart_aneg() there.

Thanks,
Feiyang

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