linux-kernel - Re: [PATCH v3] arm64: dts: freescale: imx93-phycore-som: Delay the phy reset by a gpio

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Message-ID: <8e448625-b4ad-4bf1-8930-6fecdedb1d8d@lunn.ch>
Date: Mon, 2 Jun 2025 04:09:07 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Christoph Stoidner <C.Stoidner@...tec.de>
Cc: Stefan Wahren <wahrenst@....net>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"imx@...ts.linux.dev" <imx@...ts.linux.dev>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"upstream@...ts.phytec.de" <upstream@...ts.phytec.de>
Subject: Re: [PATCH v3] arm64: dts: freescale: imx93-phycore-som: Delay the
 phy reset by a gpio

On Fri, May 30, 2025 at 01:40:38PM +0000, Christoph Stoidner wrote:
> 
> 
> On Mi, 2025-05-28 at 21:29 +0200, Andrew Lunn wrote:
> > > Yes, that's what I measured. For analysis, I added some
> > > debug outputs
> > > to
> > > the phy reset and the 1st phy register access. And as I can see,
> > > the
> > > phy register access happens when userland sets up the network:
> > 
> > Please repeat the measurements with NFS root.
> > 
> > You will find that the kernel brings the interface up right have
> > register_netdev() is called, and starts transmitting. It can happen
> > before register_netdev() even returns.
> 
> Thanks for that hint. As you said, with nfs root the register access
> happens much earlier. I measured:
> 
>        [   1.713185] DEB-PHY: mdio reset exeucted
>        ...
>        ...
>        ...
>        [   2.672892] DEB-PHY: register access
> 
> However, the delta time of 0.959707s (9597ms) still meets the T2
> ("prior to MDC preamble for register access") that is defined in the
> PHY's datasheet with 2ms.

I agree it is long enough, but i'm also surprised how slow the kernel
was. Are you using a fixed IP address, or dhcp?

	Andrew