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[176.222.226.2]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-43970d3ff1csm8365704f8f.20.2026.02.21.18.32.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 21 Feb 2026 18:32:47 -0800 (PST) Message-ID: <0308e736-c3e7-45d2-86f7-e729af9cb487@gmail.com> Date: Sun, 22 Feb 2026 03:32:45 +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: Daniel Golle , Qingfang Deng , SkyLake Huang Cc: Andrew Lunn , 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: Content-Language: en-US From: =?UTF-8?Q?Jakub_Van=C4=9Bk?= In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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. Best regards, Jakub On 2/22/26 00:46, Jakub Vaněk wrote: > The YT8821 PHY responds on two MDIO addresses by default: the address > selected by its strapping pins and the broadcast address 0. > > On platforms where another PHY is hardwired to respond only on address 0 > (e.g. the internal Gigabit PHY in the MediaTek MT7981B SoC), this can lead > to MDIO bus conflicts. The YT8821 may incorrectly respond to transactions > intended for the other PHY, leaving it in an inconsistent state. The > following issues were observed on a Cudy M3000 router: > > - Achieving just 100 Mbps speeds on gigabit links. Dmesg would show > messages like > > [ 133.997177] YT8821 2.5Gbps PHY mdio-bus:01: Downshift occurred from negotiated speed 1Gbps to actual speed 100Mbps, check cabling! > [ 134.009400] mtk_soc_eth 15100000.ethernet eth0: Link is Up - 100Mbps/Full - flow control off > > - Having the PHY report that the link is up, yet no data would flow. > - The YT8821 would be affected by an "ip link set dev eth1 down" > command aimed at the other PHY.