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[176.222.226.2]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-483a316eb08sm195961615e9.0.2026.02.21.20.22.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 21 Feb 2026 20:22:56 -0800 (PST) Message-ID: <740e8351-d8a5-4f4c-91e4-c278e4b7d248@gmail.com> Date: Sun, 22 Feb 2026 05:22:55 +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 Cc: Daniel Golle , Qingfang Deng , SkyLake Huang , Frank , Heiner Kallweit , Russell King , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Sai Krishna , netdev@vger.kernel.org, linux-kernel@vger.kernel.org References: <0308e736-c3e7-45d2-86f7-e729af9cb487@gmail.com> <3e64d8d1-87c1-45e0-9556-0ca844a90f73@lunn.ch> Content-Language: en-US From: =?UTF-8?Q?Jakub_Van=C4=9Bk?= In-Reply-To: <3e64d8d1-87c1-45e0-9556-0ca844a90f73@lunn.ch> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 2/22/26 04:35, Andrew Lunn wrote: > On Sun, Feb 22, 2026 at 03:32:45AM +0100, Jakub Vaněk wrote: >> Hello Daniel, Qingfang, SkyLake, >> >> do you happen to know if the MediaTek Gigabit PHY in the MT7981B >> can be remapped to a MDIO address other than address 0? >> >> I wasn't able to find public documentation describing the registers >> of internal PHY or whether its MDIO address is configurable. >> >> Being able to move the internal PHY off address 0 in U-Boot could be >> a better way of resolving a MDIO address conflict between the internal >> PHY and the broadcast address used by an external Motorcomm YT8821 PHY. >> >> Any pointers would be appreciated. > > Even if you can avoid the conflict, you still need to handle the fact > the YT8821 appears on two addresses. phylib has no idea it is the same > device in two places, so it can instantiate two struct phy_device for > it. This can cause problems, i think suspend/resume will break, etc. I had hoped this would not happen on the Cudy router. The MediaTek Ethernet subsystem driver uses of_mdiobus_register(), so PHY address 0 should not be probed unless it is explicitly described in the device tree. That said, I agree that with mdiobus_register() this would still be an issue. I was also hoping that moving the internal PHY would provide more flexibility in the device tree description of the YT8821. If the workaround were implemented in U-Boot by writing YT8821 MDIO registers at boot time, Linux would not be able to assert the YT8821 reset pin without losing that workaround. Jakub > There is nothing in IEEE 802.3 clause 22 or 45 that allows for this > behaviour. So rather than living with all the issues it causes, you > really do want to get the PHY into standards conformance. > > Andrew