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

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Message-ID: <aLAumWuFtJrSi7Mv@ninjato>
Date: Thu, 28 Aug 2025 12:25:29 +0200
From: Wolfram Sang <wsa+renesas@...g-engineering.com>
To: Prabhakar <prabhakar.csengg@...il.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

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.

Tested-by: Wolfram Sang <wsa+renesas@...g-engineering.com>

Thanks for this fix!


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