netdev - Re: [PATCH] net: stmmac: dwmac-imx: pause the TXC clock in fixed-link

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Date: Wed, 26 Jul 2023 14:58:49 +0300
From: Vladimir Oltean <olteanv@...il.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: Shenwei Wang <shenwei.wang@....com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	Shawn Guo <shawnguo@...nel.org>, NXP Linux Team <linux-imx@....com>,
	Russell King <linux@...linux.org.uk>,
	Giuseppe Cavallaro <peppe.cavallaro@...com>,
	Alexandre Torgue <alexandre.torgue@...s.st.com>,
	Jose Abreu <joabreu@...opsys.com>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>, netdev@...r.kernel.org,
	linux-stm32@...md-mailman.stormreply.com,
	linux-arm-kernel@...ts.infradead.org, imx@...ts.linux.dev,
	Frank Li <frank.li@....com>
Subject: Re: [PATCH] net: stmmac: dwmac-imx: pause the TXC clock in fixed-link

Hi Andrew,

On Wed, Jul 26, 2023 at 10:32:00AM +0200, Andrew Lunn wrote:
> On Tue, Jul 25, 2023 at 02:49:31PM -0500, Shenwei Wang wrote:
> > When using a fixed-link setup, certain devices like the SJA1105 require a
> > small pause in the TXC clock line to enable their internal tunable
> > delay line (TDL).
> 
> The SJA1105 has the problem, so i would expect it to be involved in
> the solution. Otherwise, how is this going to work for other MAC
> drivers?
> 
> Maybe you need to expose a common clock framework clock for the TXC
> clock line, which the SJA1105 can disable/enable? That then makes it
> clear what other MAC drivers need to do.
> 
>       Andrew
> 

The delicate nature of the SJA1105 bug is that as far as I understand,
the switch is not aware of the fact that its RGMII delay line went out
of whack. Its port MII status registers say that they're okay.

Also, if I understand Shenwei's workaround procedure, it deals more with
"prevention" than with "recovery". I'm not sure that (reliable) recovery
is possible. I'm trying to gather more data from NXP colleagues.