netdev - Re: [PATCH 2/4] phy: s32g: Add serdes subsystem phy

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Message-ID: <aXtwfj1vqB1cXKFM@shell.armlinux.org.uk>
Date: Thu, 29 Jan 2026 14:36:46 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Vinod Koul <vkoul@...nel.org>
Cc: Vincent Guittot <vincent.guittot@...aro.org>, neil.armstrong@...aro.org,
	Simon Horman <horms@...nel.org>, krzk+dt@...nel.org,
	conor+dt@...nel.org, ciprianmarian.costea@....nxp.com, s32@....com,
	p.zabel@...gutronix.de, ghennadi.procopciuc@....com,
	Ionut.Vicovan@....com, linux-phy@...ts.infradead.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, netdev@...r.kernel.org,
	Frank.li@....com
Subject: Re: [PATCH 2/4] phy: s32g: Add serdes subsystem phy

On Thu, Jan 29, 2026 at 08:00:38PM +0530, Vinod Koul wrote:
> On 29-01-26, 13:51, Russell King (Oracle) wrote:
> > On Thu, Jan 29, 2026 at 02:36:01PM +0100, Vincent Guittot wrote:
> > > On Thu, 29 Jan 2026 at 14:23, Russell King (Oracle)
> > > <linux@...linux.org.uk> wrote:
> > > >
> > > > On Thu, Jan 29, 2026 at 02:01:13PM +0100, Vincent Guittot wrote:
> > > > > yes, the usual pattern is :
> > > > > - phy_set_mode_ext()
> > > > > - then phy_power_on()
> > > > > but I can add an additional check
> > > >
> > > > Please read Documentation/driver-api/phy/phy.rst section "Order of API
> > > > calls" which suggests phy_set_mode_ext() after phy_power_on().
> > > 
> > > Fair enough.
> > > That being said, all pcie drivers  that use phy_set_mode_ext(), call
> > > it before phy_power_on()
> > 
> > It looks like many ethernet drivers do the same, so I think maybe the
> > generic PHY documentation is incorrect or misleading, or is expressing
> > a preference that almost no one follows. Something for the generic PHY
> > maintainers to look at and/or comment on.
> 
> I would feel it makes sense to configure the mode first and then power
> the phy up. As commented above yes it looks like apart from one tegra
> driver rest seem to do it this way.
> 
> Lets update the documentation

Please also indicate in the documentation whether changing the submode
of the serdes (particularly for ethernet) is permitted without doing a
phy_power_down()..phy_power_up() dance around the phy_set_mode_ext()
call.

Thanks.

-- 
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