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

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Message-ID: <78ec24d09d129d52d3442f6319cf1ef5b6ce7f3d.camel@phytec.de>
Date: Mon, 2 Jun 2025 11:46:14 +0000
From: Christoph Stoidner <C.Stoidner@...tec.de>
To: Andrew Lunn <andrew@...n.ch>
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

Hi Andrew,

On Mo, 2025-06-02 at 04:09 +0200, Andrew Lunn wrote:
> 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?

I use a fixed IP address.

But isn't the bringup of ethernet+phy interface one of the last things
that happens during the kernel boot-up?

When I boot my system from sd-card, I can see that mounting the rootfs
on the sdcard occurs at about 2500ms after kernel start:

      [    0.000000] Booting Linux on physical CPU 0x0000000000 ...
                ...
                ...
                ...
      [    2.538013] EXT4-fs (mmcblk1p2): mounted filesystem a500e519-
d77b-471c-8215-e4f51236aaaa r/w with ordered data mode. Quota mode:
none.
      [    2.550189] VFS: Mounted root (ext4 filesystem) on device
179:98.
      [    2.556871] devtmpfs: mounted
      [    2.562733] Freeing unused kernel memory: 4032K

And thats very near to what I saw with NFS root (to remember: 2672ms
from kernel start). So I feel that patch itself and its corresponding 
measured timings are valid.

However, what timing would you expect?

Thanks, 
Christoph

> 
>  Andrew