netdev - Re: [PATCH net-next v2] net: pcs: rzn1-miic: Correct MODCTRL register offset

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Message-ID: <CA+V-a8ufD4uH=9FYz+-MCeCVZb53Hja5s=LNhcr3Psi6o0yBWw@mail.gmail.com>
Date: Thu, 28 Aug 2025 11:30:36 +0100
From: "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To: Wolfram Sang <wsa+renesas@...g-engineering.com>
Cc: Clément Léger <clement.leger@...tlin.com>, 
	Andrew Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>, 
	Russell King <linux@...linux.org.uk>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Geert Uytterhoeven <geert+renesas@...der.be>, linux-renesas-soc@...r.kernel.org, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Biju Das <biju.das.jz@...renesas.com>, 
	Fabrizio Castro <fabrizio.castro.jz@...esas.com>, 
	Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>, stable@...nel.org
Subject: Re: [PATCH net-next v2] net: pcs: rzn1-miic: Correct MODCTRL register offset

Hi Wolfram,

On Thu, Aug 28, 2025 at 11:25 AM Wolfram Sang
<wsa+renesas@...g-engineering.com> wrote:
>
> On Wed, Aug 20, 2025 at 06:09:13PM +0100, Prabhakar wrote:
> > From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> >
> > Correct the Mode Control Register (MODCTRL) offset for RZ/N MIIC.
> > According to the R-IN Engine and Ethernet Peripherals Manual (Rev.1.30)
> > [0], Table 10.1 "Ethernet Accessory Register List", MODCTRL is at offset
> > 0x8, not 0x20 as previously defined.
> >
> > Offset 0x20 actually maps to the Port Trigger Control Register (PTCTRL),
> > which controls PTP_MODE[3:0] and RGMII_CLKSEL[4]. Using this incorrect
> > definition prevented the driver from configuring the SW_MODE[4:0] bits
> > in MODCTRL, which control the internal connection of Ethernet ports. As
> > a result, the MIIC could not be switched into the correct mode, leading
> > to link setup failures and non-functional Ethernet ports on affected
> > systems.
> >
> > [0] https://www.renesas.com/en/document/mah/rzn1d-group-rzn1s-group-rzn1l-group-users-manual-r-engine-and-ethernet-peripherals?r=1054571
> >
> > Fixes: 7dc54d3b8d91 ("net: pcs: add Renesas MII converter driver")
> > Cc: stable@...nel.org
> > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> > Reviewed-by: Wolfram Sang <wsa+renesas@...g-engineering.com>
>
> I had a look now. Because the bootloader of my N1D board already set up
> MODCTRL correctly, this write to the wrong register went unnoticed. I
> verified that the now correctly written value (depending on DT config)
> matches the value previously set by the bootloader. As a result,
> everything keeps working. We were lucky. Or unlucky. Depending how you
> look at it.
>
Thank you for testing it. I'll send a v3 soon with `net-next` dropped
from the subject.

Cheers,
Prabhakar