From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f49.google.com (mail-wm1-f49.google.com [209.85.128.49]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C33253D565C for ; Thu, 16 Apr 2026 14:25:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.49 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776349532; cv=none; b=XpV7T8xt3NwI2MsuUj8Z899ahPyLg3x0BRGCEWySBsmw2ChRJKdicLEuL6/1W9I9CWsoe4vw0JBQTvbDS2do8E6LMNcCe3VZ5mNIAGViEsdlhqvyHgYz97OrJlZ1YlYVwUHDfhrVBzT3zajVeah+ydQ8BRWr7GPsEx6dajstwzE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776349532; c=relaxed/simple; bh=Mah8Cmz6ZMkLKwtTNEnHpt5iWh2TaRLSHEFPfpzNWFY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=hcz8J2P/Ef1Vhwm5uPCIIEv2aa4NWSvGm6Cxlyd2cXqNII+cvWoCqW7+bJ6h1V1KJGpv6luheieZ2TDRABuo+1PBkaS1bJxWjdTRJe3lsv/Dvj6ZWLnbhKyYKZ3j+zLXuHwZ0ztV8s/fnPDYoKjQ5VweHFbiqMoB9P47vpEzG0k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=kWUWdcGW; arc=none smtp.client-ip=209.85.128.49 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="kWUWdcGW" Received: by mail-wm1-f49.google.com with SMTP id 5b1f17b1804b1-48334ee0aeaso78721175e9.1 for ; Thu, 16 Apr 2026 07:25:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1776349529; x=1776954329; darn=vger.kernel.org; h=content-transfer-encoding:in-reply-to:from:content-language :references:cc:to:subject:user-agent:mime-version:date:message-id :from:to:cc:subject:date:message-id:reply-to; bh=YY91CEdfGmuARnJ03T8w9/266qNTo7bDb9b4TzuMo0s=; b=kWUWdcGWo/JhJA2fA71lJrGoLTcbpov7ptQsLz2OdiGYP/K9GhdRS5SKhLGY1lRAay 0p7XAS40v9lOvgxdA9bNiQOYc2lSDFKMqVqftlRgZ6fcAGLqK3dtJOwxk1Aj/Fg9y9Eo Nrl7ZtllQmBDiMc2muGng7KtXQBQVM38O+Z6utuqTAaJNAx+4hDn2yvQ8XsVfzAQlEf0 dqufoS1bogTGY+gyKArpB5mmRWiS/WTsEWIG0f0MKQFIqhS0001iSRUj3vCYDa+Smm5E FW20hlPUaReZaI2ffNHvsGBRBqlHwyUH3bIQdY+tSZ3wAj4xS50ZIQlFaa8661YXmF/G Sbog== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1776349529; x=1776954329; h=content-transfer-encoding:in-reply-to:from:content-language :references:cc:to:subject:user-agent:mime-version:date:message-id :x-gm-gg:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=YY91CEdfGmuARnJ03T8w9/266qNTo7bDb9b4TzuMo0s=; b=HgcqqEKkH2mWop00ki0vuECHiUa7HSZD38wrICx1iHia4YbVlxGgH+ApQfuN5oqTGx muPuepovFd5Y11JWWOSdA31/tGRCpSbzukwR6RIxlJNQmGrcNjOF+Ti7IQyyYewX4BD+ qROvbcP0RyvQe+GCsbz3YGN2Olw2ym7RZXewFwVV3QM2TkGrqV0reo2UBHRee2Ao5Tz3 Z1jHIA+KyZSpckD1GhJZ/HUaE+rThutLKIPItAG/+1EsiqUKb7yq4da3ZTkowvc6MCd2 R21EbizwkAoBZpP3OWideXXID6AG0LHxtMRDOhQGsIcmT+ElYQmzuewRpVCuSbYOP37y 1IgQ== X-Forwarded-Encrypted: i=1; AFNElJ8S7oRfkq0QTxcVahmBf5VLcN+Hdt+kH9E8xxB9vYRd24PJ0wv3Sjth2GKe/8/rnhjo7qPARVQSdsQ7zug=@vger.kernel.org X-Gm-Message-State: AOJu0YxeIUH2HhsE00RThsG2N7Wt+RrhkPpMkUbCVIi7qD7h09aN9AsB IZT3EHzQusoWN60cumYQ99FxNjooYCj/DE5vRf3zkrPeBaaPtjGdo0at X-Gm-Gg: AeBDieueBQQ3z/2xwLlImHA98uKz8nnJW678VTTfiPE1Ro2lbGYkNqCvitgtDUle486 X7folX9Qr0rREWZ5pqBEs44EnqmKMB/KKgjEggfD9s6NSDxQkGbjJGnWnttpIPowCMu7/jOK3e9 vARzxfI1V1jqrg87vtpFeSSY9I2UWqn/+D7hwXqSqKlWR9WywnkR4nv2/AiyXF4H9eNzPrzmuZT UI+tYwZ2k/YRuSizN1pe1pI+6qG1HHgUhU+zI7r0EIEptPGwvJHeR/NsVR2xcPrxE30L+8KgCWO iIyRGmO98rImy9vkZ+2W7bzcwYsiRGFBIFXxBDhf1jYfox8Xbtq9JH35L2X5Rix3VcCfDb83yKV cui+UcTefUPdpYlkVtZVHHpUoEtrUlrVfWAznZNm+0KDOtzBNE/0icW5FuR6PvBIhButUpaZwgj sTFExnPjuwfMp/ji1alaE43Dc7otqAxJqCgA4KhDi0ftCOxOchdxgH0LOWkXRQPNcg1MH4coeOf AbBhpfVQjtPdfzaYAX5 X-Received: by 2002:a05:600c:8b27:b0:488:af7f:775f with SMTP id 5b1f17b1804b1-488d68766c7mr343666655e9.18.1776349528895; Thu, 16 Apr 2026 07:25:28 -0700 (PDT) Received: from [10.1.4.108] (cust-east-par-46-193-119-166.cust.wifirst.net. [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: linux-kernel@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