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

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Message-ID: <Z-r7c1bAHJK48xhD@shell.armlinux.org.uk>
Date: Mon, 31 Mar 2025 21:30:43 +0100
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Da Xue <da@...sconfused.com>
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 03:09:00PM -0400, Da Xue wrote:
> 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.

Which interface mode do we think this affects?

As a suggestion, maybe call it:

REG2_<interfacemode>_EN

and possibly add a comment "This bit is documented as reserved, but
needs to be set so that <interfacemode> can pass traffic. This is
an unofficial name."

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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