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

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Message-ID: <bf0eb48fc72f4b0abbf62077c2f1fe4438579746.camel@phytec.de>
Date: Mon, 26 May 2025 10:04:17 +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 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).
> > 
> > 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
> > > > 
>