From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.tipi-net.de (mail.tipi-net.de [194.13.80.246]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EB5F7213E9C; Mon, 1 Jun 2026 15:43:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=194.13.80.246 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780328617; cv=none; b=KWwZvOLULVvEJ1B3S7pLcuZ4fgrlGm5SzQASwU0JvEBsneHamtuNiTZjSV0wmUHmAEueBG/bIzduIBTIIyy+oD8cRl9dTiAF0Ilbo+s60o8X9q7nj4JS6ME61Xh1RfDOQmzq4+6AnZ1PE0S1faWx9cbOfw0PGBWJ/DBoBbMNsmE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780328617; c=relaxed/simple; bh=QZ5A64AbPHpTabE09qPlAkl3BR7KJdWRnkf/p+FiGfo=; h=MIME-Version:Date:From:To:Cc:Subject:In-Reply-To:References: Message-ID:Content-Type; b=tCqUlf3ArGWeFsCmO3HY+b/l5iOepTmclOYevhTDBE4kU/xvBfCmKvXIBjcYCy8UxWoMlaA1qXDRvMXowCDWrMSxfvaF2biH6vGZ8yv5muN99NLWFjtQOVmtxZFHrx+okMqQ4XDTpJOvXBIgZq0wg0gxlbhXcPZykds8m3QomlI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=tipi-net.de; spf=pass smtp.mailfrom=tipi-net.de; dkim=pass (2048-bit key) header.d=tipi-net.de header.i=@tipi-net.de header.b=m1zwpgwx; arc=none smtp.client-ip=194.13.80.246 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=tipi-net.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=tipi-net.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=tipi-net.de header.i=@tipi-net.de header.b="m1zwpgwx" Received: from [127.0.0.1] (localhost [127.0.0.1]) by localhost (Mailerdaemon) with ESMTPSA id 8364BA4C08; Mon, 1 Jun 2026 17:43:27 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=tipi-net.de; s=dkim; t=1780328610; h=from:subject:date:message-id:to:cc:mime-version:content-type: content-transfer-encoding:in-reply-to:references; bh=uitTw5r+FjzP/teK02MYNuvZ6+HKUF13Y6sZDAeV5F4=; b=m1zwpgwxcHie/GpolPuWxORP8ZWo7JykVhePa6EwJRiUYkKOyvNcAV5efoKt1VVu1Ry3uF 3n1Rsn0Mm3YS1quwx2zUacH0jNcOdvg0eZBpRyxIHz9+w1B2kfzcZRZrCG5qIQIk3Kh+G0 bjcFM2D4MP0qBbljcMaoMdQ9QXKHL+k/hOOck6/jFfq5z2kxT1Zy73k8a5fUBXUE6R39cZ GZCLsu0emmO+ZvLa1ZAPisFxAFTXGpbzdjfI0woVbmL4ZR7+Jq0ayQjXy6wDi43o8t56sb vDpdtr/4bhDIczXM+Y4MUIrk0u8YGhEd+cP5nWRGXD5eMRbz0mtqsOjFq0teiA== Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Date: Mon, 01 Jun 2026 17:43:27 +0200 From: Nicolai Buchwitz To: Fidelio Lawson Cc: Woojung Huh , UNGLinuxDriver@microchip.com, Andrew Lunn , Vladimir Oltean , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Marek Vasut , Maxime Chevallier , Simon Horman , Heiner Kallweit , Russell King , Tristram Ha , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Fidelio Lawson , Marek Vasut Subject: Re: [PATCH net-next v9 0/3] ksz87xx: add support for low-loss cable equalizer errata In-Reply-To: <20260601-ksz87xx_errata_low_loss_connections-v9-0-fdbbb15592cb@exotec.com> References: <20260601-ksz87xx_errata_low_loss_connections-v9-0-fdbbb15592cb@exotec.com> Message-ID: <018a05a2cfffe4f9a7df608676ec554d@tipi-net.de> X-Sender: nb@tipi-net.de Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Last-TLS-Session-Version: TLSv1.3 Hi Fidelio On 1.6.2026 17:19, Fidelio Lawson wrote: > Hello, > > This patch implements the KSZ87xx short cable erratum > described in Microchip document DS80000687C for KSZ87xx switches > and the following support article: > > Link: > https://support.microchip.com/s/article/Solution-for-Using-CAT-5E-or-CAT-6-Short-Cable-with-a-Link-Issue-for-the-KSZ8795-Family > > According to the erratum, the embedded PHY receiver in KSZ87xx switches > is > tuned by default for long, high-loss Ethernet cables. When operating > with > short or low-loss cables (for example CAT5e or CAT6), the PHY equalizer > may > over-amplify the incoming signal, leading to internal distortion and > link > establishment failures. > > Microchip documents two independent mechanisms to mitigate this issue: > adjusting the receiver low‑pass filter bandwidth and reducing the DSP > equalizer initial value. These registers are located in the switch’s > internal LinkMD table and cannot be accessed directly through a > stand‑alone PHY driver. > > To keep the PHY‑facing API clean, this series models the erratum > handling > as vendor‑specific Clause 22 PHY registers, virtualized by the KSZ8 DSA > driver. Accesses are intercepted by ksz8_r_phy() / ksz8_w_phy() and > translated into the appropriate indirect LinkMD register writes. The > erratum affects the shared PHY analog front‑end and therefore applies > globally to the switch. > > Based on review feedback, the user‑visible interface is kept > deliberately > simple and predictable: > > - A boolean “short‑cable” PHY tunable applies a documented and > conservative preset (LPF bandwidth 62MHz, DSP EQ initial value 0). > This is the recommended KISS interface for the common short‑cable > scenario. > > - Two additional integer PHY tunables allow advanced or experimental > tuning of the LPF bandwidth and the DSP EQ initial value. These > controls are orthogonal, have no ordering requirements, and simply > override the corresponding setting when written. > > The tunables act as simple setters with no implicit state machine or > invalid combinations, avoiding surprises for userspace and not relying > on extended error reporting or netlink ethtool support. > > This series contains: > > 1. Support for the KSZ87xx low‑loss cable erratum in the KSZ8 DSA > driver, > including the short‑cable preset and orthogonal tuning controls. > > 2. Addition of vendor‑specific PHY tunable identifiers for the > short‑cable preset, LPF bandwidth, and DSP EQ initial value. > > 3. Exposure of these tunables through the Micrel PHY driver via > get_tunable / set_tunable callbacks. > > This version follows the design agreed upon during v3 review and > reworks the interface accordingly. > > This series is based on net-next. > > Signed-off-by: Fidelio Lawson > --- > Changes in v9: > - Drop incorrect Fixes tag > - Fix typo in comment > - Link to v8: > https://patch.msgid.link/20260601-ksz87xx_errata_low_loss_connections-v8-0-cfa102cf62c0@exotec.com Please don't re-send patched within the 24h grace period as stated in the netdev FAQ [1] Thanks Nicolai [1] https://www.kernel.org/doc/html/v6.1/process/maintainer-netdev.html#tl-dr