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Thu, 12 Sep 2024 11:30:29 -0700 (PDT) Received: from [10.67.48.245] ([192.19.223.252]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-45822f60a4csm55521151cf.62.2024.09.12.11.30.27 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 12 Sep 2024 11:30:29 -0700 (PDT) Message-ID: <7736f0f2-8a99-4329-b290-089454d56e36@gmail.com> Date: Thu, 12 Sep 2024 11:30:26 -0700 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net-next 1/7] net: phy: allow isolating PHY devices To: Maxime Chevallier , davem@davemloft.net Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, thomas.petazzoni@bootlin.com, Andrew Lunn , Jakub Kicinski , Eric Dumazet , Paolo Abeni , Russell King , linux-arm-kernel@lists.infradead.org, Christophe Leroy , Herve Codina , Heiner Kallweit , Vladimir Oltean , =?UTF-8?Q?Marek_Beh=C3=BAn?= , =?UTF-8?Q?K=C3=B6ry_Maincent?= , Oleksij Rempel References: <20240911212713.2178943-1-maxime.chevallier@bootlin.com> <20240911212713.2178943-2-maxime.chevallier@bootlin.com> Content-Language: en-US From: Florian Fainelli Autocrypt: addr=f.fainelli@gmail.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240912_113031_873625_774B8F0A X-CRM114-Status: GOOD ( 16.50 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 9/11/24 14:27, Maxime Chevallier wrote: > The 802.3 specifications describes the isolation mode as setting the > PHY's MII interface in high-impedance mode, thus isolating the PHY from > that bus. This effectively breaks the link between the MAC and the PHY, > but without necessarily disrupting the link between the PHY and the LP. > > This mode can be useful for testing purposes, but also when there are > multiple PHYs on the same MII bus (a case that the 802.3 specification > refers to). > > In Isolation mode, the PHY will still continue to respond to MDIO > commands. > > Introduce a helper to set the phy in an isolated mode. > > Signed-off-by: Maxime Chevallier Not sure where that comment belongs so I will put it here, one thing that concerns me is if you have hardware that is not strapped to be isolated by default, and the PHY retains the state configured by Linux, such that the PHY is in isolation mode. A boot loader that is not properly taking the PHY out of isolation mode would be unavailable to use it and that would be a bug that Linux would likely be on the hook to fix. Would recommend adding a phy_shutdown() method which is called upon reboot/kexec and which, based upon a quirk/flag can ensure that the isolation bit is cleared. -- Florian