linux-kernel - Re: [PATCH v2] net: mdio: mux-meson-gxl: set 28th bit in eth_reg2

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Message-ID: <CACdvmAijY=ovZBgwBFDBne5dJPHrReLTV6+1rJZRxxGm42fcMA@mail.gmail.com>
Date: Mon, 31 Mar 2025 15:09:00 -0400
From: Da Xue <da@...sconfused.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: Andrew Lunn <andrew@...n.ch>, Neil Armstrong <neil.armstrong@...aro.org>, 
	Martin Blumenstingl <martin.blumenstingl@...glemail.com>, Kevin Hilman <khilman@...libre.com>, 
	linux-kernel@...r.kernel.org, stable@...r.kernel.org, 
	Da Xue <da@...re.computer>, Eric Dumazet <edumazet@...gle.com>, netdev@...r.kernel.org, 
	Jerome Brunet <jbrunet@...libre.com>, Jakub Kicinski <kuba@...nel.org>, 
	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 v2] net: mdio: mux-meson-gxl: set 28th bit in eth_reg2

On Mon, Mar 31, 2025 at 9:55 AM Russell King (Oracle)
<linux@...linux.org.uk> wrote:
>
> On Mon, Mar 31, 2025 at 03:43:26PM +0200, Andrew Lunn wrote:
> > On Mon, Mar 31, 2025 at 07:44:20AM +0000, Christian Hewitt wrote:
> > > From: Da Xue <da@...re.computer>
> > >
> > > This bit is necessary to enable packets on the interface. Without this
> > > bit set, ethernet behaves as if it is working, but no activity occurs.
> > >
> > > The vendor SDK sets this bit along with the PHY_ID bits. U-boot also
> > > sets this bit, but if u-boot is not compiled with networking support
> > > the interface will not work.
> > >
> > > Fixes: 9a24e1ff4326 ("net: mdio: add amlogic gxl mdio mux support");
> > > Signed-off-by: Da Xue <da@...re.computer>
> > > Signed-off-by: Christian Hewitt <christianshewitt@...il.com>
> > > ---
> > > Resending on behalf of Da Xue who has email sending issues.
> > > Changes since v1 [0]:
> > > - Remove blank line between Fixes and SoB tags
> > > - Submit without mail server mangling the patch
> > > - Minor tweaks to subject line and commit message
> > > - CC to stable@...r.kernel.org
> > >
> > > [0] https://patchwork.kernel.org/project/linux-amlogic/patch/CACqvRUbx-KsrMwCHYQS6eGXBohynD8Q1CQx=8=9VhqZi13BCQQ@mail.gmail.com/
> > >
> > >  drivers/net/mdio/mdio-mux-meson-gxl.c | 3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/net/mdio/mdio-mux-meson-gxl.c b/drivers/net/mdio/mdio-mux-meson-gxl.c
> > > index 00c66240136b..fc5883387718 100644
> > > --- a/drivers/net/mdio/mdio-mux-meson-gxl.c
> > > +++ b/drivers/net/mdio/mdio-mux-meson-gxl.c
> > > @@ -17,6 +17,7 @@
> > >  #define  REG2_LEDACT               GENMASK(23, 22)
> > >  #define  REG2_LEDLINK              GENMASK(25, 24)
> > >  #define  REG2_DIV4SEL              BIT(27)
> > > +#define  REG2_RESERVED_28  BIT(28)
> >
> > It must have some meaning, it cannot be reserved. So lets try to find
> > a better name.
>
> Indeed, that was my thoughts as well, but Andrew got his reply in
> before I got around to replying!

The datasheets don't have much in the way of information about this
register bit. The Amlogic GXL datasheet is notoriously inaccurate.

ETH_REG2 0XC8834558
29:28 R 0x1 reserved

It claims the bit is read only while the BSP hard codes the setting of
this register. I am open to any name for this register bit.
This is the only thing holding up distro netbooting for these very
popular chip family.

>
> --
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
> FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!
>
> _______________________________________________
> linux-amlogic mailing list
> linux-amlogic@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-amlogic

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