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[176.222.226.2]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-483a31bc0e3sm262435565e9.5.2026.02.23.12.06.41 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 23 Feb 2026 12:06:41 -0800 (PST) Message-ID: Date: Mon, 23 Feb 2026 21:06:40 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net v1] net: phy: motorcomm: yt8821: disable MDIO broadcast address 0 To: Andrew Lunn , Russell King Cc: Frank , Heiner Kallweit , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Sai Krishna , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Daniel Golle References: <3e9812a5-401b-400d-9d9b-eec8ec8d0acf@lunn.ch> Content-Language: en-US From: =?UTF-8?Q?Jakub_Van=C4=9Bk?= In-Reply-To: <3e9812a5-401b-400d-9d9b-eec8ec8d0acf@lunn.ch> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Hello, An alternative approach was suggested to me earlier today: changing the probing order in (of_)mdiobus_register() so that PHY address 0 is always probed last. The offending PHYs would be reconfigured to not listen for broadcasts on address 0 either via the PHY driver .probe callbacks or via non-board-specific PHY fixups. Do you think such an approach could reliably avoid the address-0 conflict, and would a patch along these lines be acceptable upstream? This issue does not appear to be specific to the Motorcomm YT8821. I have found other PHYs that also respond on MDIO address 0 in addition to their strapped address, including: * Realtek RTL8221B and RTL8211F PHYs, * Micrel KSZ8081, where this is acknowledged in commit 57a38effa598 ("net: phy: micrel: disable broadcast for KSZ8081/KSZ8091") My understanding is that this behavior may stem from differing interpretations of IEEE 802.3-2005 Clause 22.2.4.5.5. As I read it, the clause requires a PHY connected via a specific cable to always respond on address 0; some vendors appear to have interpreted this as the address 0 being a reserved broadcast address. I also received some feedback on replacing the bootloader in various routers. While the U-Boot can be replaced in the Cudy M3000, this may not be the case for all manufacturers. On those platforms, a kernel- level fix would be necessary, although it could remain as a downstream patch in OpenWrt if the fix is unsuitable for mainline. What are your thoughts on this? Best regards, Jakub