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

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Message-ID: <517be266ebc3b55da53372a76a139245f8945cd8.camel@phytec.de>
Date: Wed, 28 May 2025 18:30:48 +0000
From: Christoph Stoidner <C.Stoidner@...tec.de>
To: Stefan Wahren <wahrenst@....net>, Andrew Lunn <andrew@...n.ch>
CC: 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 Mo, 2025-05-26 at 14:14 +0200, Stefan Wahren wrote:
> Am 26.05.25 um 12:04 schrieb Christoph Stoidner:
> > On Mo, 2025-05-26 at 11:24 +0200, Stefan Wahren wrote:
> > > Am 26.05.25 um 11:09 schrieb Christoph Stoidner:
> > > > Hi Stefan,
> > > > 
> > > > On Mo, 2025-05-26 at 08:44 +0200, Stefan Wahren wrote:
> > > > > Hi Andrew,
> > > > > hi Christoph
> > > > > 
> > > > > Am 24.05.25 um 19:44 schrieb Andrew Lunn:
> > > > > > > diff --git a/arch/arm64/boot/dts/freescale/imx93-phycore-
> > > > > > > som.dtsi
> > > > > > > b/arch/arm64/boot/dts/freescale/imx93-phycore-som.dtsi
> > > > > > > index 88c2657b50e6..b481097f08a4 100644
> > > > > > > --- a/arch/arm64/boot/dts/freescale/imx93-phycore-
> > > > > > > som.dtsi
> > > > > > > +++ b/arch/arm64/boot/dts/freescale/imx93-phycore-
> > > > > > > som.dtsi
> > > > > > > @@ -68,6 +68,8 @@ mdio: mdio {
> > > > > > >      ethphy1: ethernet-phy@1 {
> > > > > > >      compatible = "ethernet-phy-ieee802.3-c22";
> > > > > > >      reg = <1>;
> > > > > > > + reset-gpios = <&gpio4 23 GPIO_ACTIVE_HIGH>;
> > > > > > > + reset-assert-us = <30>;
> > > > > > Is there anything in the datasheet about needing a delay
> > > > > > after
> > > > > > the
> > > > > > reset? There is a DT property for this:
> > > > > > 
> > > > > >      reset-deassert-us:
> > > > > >        description:
> > > > > >          Delay after the reset was deasserted in
> > > > > > microseconds.
> > > > > > If
> > > > > >          this property is missing the delay will be
> > > > > > skipped.
> > > > > is it the time until the PHY finished its post reset
> > > > > stabilization
> > > > > (datasheet to call it T2 "reset to SMI ready")?
> > > > The T2 ("Post reset stabilization time") in the datasheet is
> > > > the
> > > > time
> > > > "prior to MDC preamble for register access", that is defined
> > > > with
> > > > 2ms.
> > > > I did not use reset-deassert-us for it, because the first
> > > > register
> > > > access does anyway occur much later (I measured 4000ms).
> Just to be sure, do you really mean 4000 milliseconds ?
> 
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:


       [   1.723298] DEB-PHY: mdio reset exeucted
       ...
       ...
       ...
       [  OK  ] Started Network Configuration.
       [   5.792705] DEB-PHY: register access


The calculated delta of 4,069407 seconds fits to what I measured with
the oscilloscope (4040ms).

Regards,
Christoph


> > > > 
> > > > And we have the same for T4, the "Post power-up stabilization
> > > > time".
> > > > It is defined with a time of 50ms as "prior to MDC preamble for
> > > > register access". But also here we just know, the register
> > > > access
> > > > happens much later - and treated it as enough.
> > > > 
> > > > Formally, this may be valid to specify the 2ms as reset-
> > > > deassert-
> > > > us.
> > > > But since the first register access is so much later, I thought
> > > > we
> > > > can
> > > > save those 2ms.
> > > > 
> > > > Are you fine with that?
> > > I don't insist on an additional "reset-deassert-us". The question
> > > was
> > > more about understanding.
> > Great, thanks for thr feedback.
> > 
> > > > Regards,
> > > > Christoph
> > > > 
> > > > 
> > > > > > Anyway:
> > > > > > 
> > > > > > Reviewed-by: Andrew Lunn <andrew@...n.ch>
> > > > > > 
> > > > > >        Andrew
> > > > > > 
>