linux-kernel - Re: [PATCH v3] net: mdio: mux-meson-gxl: set reversed bit when using internal phy

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Message-ID: <20250429120210.0aa6fa81@kernel.org>
Date: Tue, 29 Apr 2025 12:02:10 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Da Xue <da@...sconfused.com>
Cc: Simon Horman <horms@...nel.org>, Da Xue <da@...re.computer>, Andrew Lunn
 <andrew@...n.ch>, Neil Armstrong <neil.armstrong@...aro.org>, Martin
 Blumenstingl <martin.blumenstingl@...glemail.com>, Kevin Hilman
 <khilman@...libre.com>, Russell King <linux@...linux.org.uk>,
 stable@...r.kernel.org, linux-kernel@...r.kernel.org, Eric Dumazet
 <edumazet@...gle.com>, netdev@...r.kernel.org, Jerome Brunet
 <jbrunet@...libre.com>, linux-amlogic@...ts.infradead.org, Paolo Abeni
 <pabeni@...hat.com>, "David S. Miller" <davem@...emloft.net>,
 linux-arm-kernel@...ts.infradead.org, Heiner Kallweit
 <hkallweit1@...il.com>
Subject: Re: [PATCH v3] net: mdio: mux-meson-gxl: set reversed bit when
 using internal phy

On Mon, 28 Apr 2025 20:44:14 -0400 Da Xue wrote:
> > On Fri, Apr 25, 2025 at 03:20:09PM -0400, Da Xue wrote:  
> > > This bit is necessary to receive packets from the internal PHY.
> > > Without this bit set, no activity occurs on the interface.
> > >
> > > Normally u-boot sets this bit, but if u-boot is compiled without
> > > net support, the interface will be up but without any activity.
> > >
> > > The vendor SDK sets this bit along with the PHY_ID bits.  
> >
> > I'd like to clarify that:
> > Without this patch the writel the patch is modifying will clear the PHY_ID bit.
> > But despite that the system works if at some point (uboot) set the PHY_ID bit?  
> 
> Correct. If this is set once, it will work until the IP is powered
> down or reset.
> If u-boot does not set it, Linux will not set it and the IP will not work.
> If u-boot does set it, the IP will not work after suspend-resume since
> the IP is reset.
> Thus, we need to set it on the Linux side when bringing up the interface.

Added to the commit message when applying, thank you both!