netdev - Re: [PATCH net-next v6 5/8] net: phy: Immediately call adjust_link if only tx_lpi

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Message-ID: <8d48af5b-e92b-431c-9bc0-ce6ef0e0ab2e@lunn.ch>
Date: Tue, 27 Feb 2024 17:12:22 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Oleksij Rempel <o.rempel@...gutronix.de>
Cc: "Russell King (Oracle)" <linux@...linux.org.uk>,
	Florian Fainelli <florian.fainelli@...adcom.com>,
	netdev@...r.kernel.org, Clark Wang <xiaoning.wang@....com>,
	linux-kernel@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
	Shenwei Wang <shenwei.wang@....com>, Wei Fang <wei.fang@....com>,
	NXP Linux Team <linux-imx@....com>, kernel@...gutronix.de,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	Heiner Kallweit <hkallweit1@...il.com>
Subject: Re: [PATCH net-next v6 5/8] net: phy: Immediately call adjust_link
 if only tx_lpi_enabled changes

On Tue, Feb 27, 2024 at 06:35:38AM +0100, Oleksij Rempel wrote:
> On Mon, Feb 26, 2024 at 07:59:28PM +0100, Andrew Lunn wrote:
> > On Mon, Feb 26, 2024 at 05:53:31PM +0000, Russell King (Oracle) wrote:
> > > On Mon, Feb 26, 2024 at 09:50:02AM -0800, Florian Fainelli wrote:
> > > > This is the source of the concern, we don't know which MAC drivers we might
> > > > end-up breaking by calling adjust_link(link == 1) twice in a row, hopefully
> > > > none, because they should be well written to only update the parameters that
> > > > need updating, but who knows?
> > > 
> > > Just quickly... There are some (I went through a bunch.) They don't
> > > support EEE. I haven't been through all though, so there could be
> > > some which support EEE and where adjust_link() with phydev->link=true
> > > twice in a row could result in badness.
> > 
> > So i think we all agree the MAC needs to see a down/up, even if the
> > link itself never went down. Anything else is too risky and will
> > probably break something somewhere.
> 
> Means, this patch should be dropped.

No.

This patch handles the case that EEE is changed, but does not require
an auto-neg cycle. If you drop this patch, that use case breaks.

You need to extend this patch to signal to the MAC a down followed by
an up. It is a fake down, the media side never goes down, but the MAC
needs to think it has in order to keep with the usual convention that
we never call adjust_link() twice with phydev->link not changing.

   Andrew