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[46.193.119.166]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-488f0959d82sm48640365e9.7.2026.04.16.07.25.27 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 16 Apr 2026 07:25:28 -0700 (PDT) Message-ID: Date: Thu, 16 Apr 2026 16:25:27 +0200 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/3] net: dsa: microchip: implement KSZ87xx Module 3 low-loss cable errata To: Andrew Lunn Cc: Marek Vasut , Woojung Huh , UNGLinuxDriver@microchip.com, Vladimir Oltean , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Maxime Chevallier , Simon Horman , Heiner Kallweit , Russell King , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Fidelio Lawson References: <20260414-ksz87xx_errata_low_loss_connections-v3-0-0e3838ca98c9@exotec.com> <20260414-ksz87xx_errata_low_loss_connections-v3-1-0e3838ca98c9@exotec.com> <712cc46a-5ceb-4f0f-88bb-fa0a47002258@nabladev.com> <84e24758-2f59-44ca-a9b8-a46094578f83@gmail.com> <03040421-89e7-4422-9fb5-0367a34323e4@lunn.ch> Content-Language: en-US From: Fidelio LAWSON In-Reply-To: <03040421-89e7-4422-9fb5-0367a34323e4@lunn.ch> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 4/16/26 14:25, Andrew Lunn wrote: >> Yes, I think a reasonable compromise could be to expose three tunables: >> >> - a boolean "short-cable" tunable, which applies the known good settings >> (LPF 62 MHz BW, DSP EQ initial value 0). >> >> - an integer LPF bandwidth tunable, for advanced use cases where further >> tuning is needed; >> >> - an integer DSP EQ initial value tunable, for the same advanced cases. >> >> The boolean tunable would follow the KISS principle and cover the common >> scenario, while the more granular controls would remain optional. > > How do the three interact? Do you need to first enable short-cable > before you set LPG bandwidth or DSP EQ? If it is not enabled, do you > get -EINVAL? > > It seems like having extack would be useful to return informative > error messages to user space, however, that requires netlink > ethtool. And ETHTOOL_PHY_STUNABLE has not been added to netlink > ethtool yet :-( > > Andrew My intention would be to keep the interactions as simple and non-surprising as possible, and avoid requiring any particular ordering or state machine between the tunables. The boolean short-cable tunable would simply apply the preset in one step. The LPF bandwidth and DSP EQ initial value tunables would be orthogonal knobs which can be set independently at any time, regardless of whether short-cable is enabled or not. With this model, we don’t need to return -EINVAL for combinations or ordering, and userspace does not need detailed error reporting. The tunables behave more like simple setters than a mode switch, which keeps the API predictable and avoids the need for extack or netlink ethtool support at this point. Fidelio