From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2E1BAC433E1 for ; Fri, 17 Jul 2020 07:49:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 06EA120768 for ; Fri, 17 Jul 2020 07:49:47 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=earth.li header.i=@earth.li header.b="pCij9v6b" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726198AbgGQHtq (ORCPT ); Fri, 17 Jul 2020 03:49:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38800 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726105AbgGQHtq (ORCPT ); Fri, 17 Jul 2020 03:49:46 -0400 Received: from the.earth.li (the.earth.li [IPv6:2a00:1098:86:4d:c0ff:ee:15:900d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1EBAAC061755; Fri, 17 Jul 2020 00:49:46 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=earth.li; s=the; h=In-Reply-To:Content-Type:MIME-Version:References:Message-ID:Subject :Cc:To:From:Date:Sender:Reply-To:Content-Transfer-Encoding:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=GxSH3WgRcAs4BQXGeagIES8YCdrXCuFUlM7hGjVh35Y=; b=pCij9v6b1c9DzBtrS1BYXlN1ZU FbJTzahWrmUxhdKMMORQgOqP5gPLHXFbskUzmny1M2ZkQhnVdQ+w6WyCcIB7np1FHqGFAOvCupBTj RfD0Q4hCeQybP0qlBa5zVmma+dBvjeesHZoiuzQtITsBNEgSBFhWnTTyif4c26CFzlMoKCciEF46G 3zc5rUO9YUl80ii83Hhcvjul89S4q/zalLNGiTDAG+Bedswam5XVk1AW5D/hsIJFBj0m5ZhMHVhCm dAvUMV82Li3yjSP1F2MG0qieSY1coQ5SwVzFBNYthOYna6xj8VElsZS9VdFIHwKQOMTUnU2AMsXbM 8ixXfToA==; Received: from noodles by the.earth.li with local (Exim 4.92) (envelope-from ) id 1jwL7f-00033F-1W; Fri, 17 Jul 2020 08:49:35 +0100 Date: Fri, 17 Jul 2020 08:49:35 +0100 From: Jonathan McDowell To: Vladimir Oltean Cc: Jakub Kicinski , Matthew Hagan , Andrew Lunn , Vivien Didelot , Florian Fainelli , "David S. Miller" , linux@armlinux.org.uk, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, John Crispin , Rob Herring , devicetree@vger.kernel.org Subject: Re: [PATCH 2/2] dt-bindings: net: dsa: qca8k: Add PORT0_PAD_CTRL properties Message-ID: <20200717074934.GH23489@earth.li> References: <2e1776f997441792a44cd35a16f1e69f848816ce.1594668793.git.mnhagan88@gmail.com> <20200716150925.0f3e01b8@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> <20200716223822.yptldqqn36fbp2i7@skbuf> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200716223822.yptldqqn36fbp2i7@skbuf> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: devicetree-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org On Fri, Jul 17, 2020 at 01:38:22AM +0300, Vladimir Oltean wrote: > On Thu, Jul 16, 2020 at 03:09:25PM -0700, Jakub Kicinski wrote: > > On Mon, 13 Jul 2020 21:50:26 +0100 Matthew Hagan wrote: > > > +- qca,sgmii-rxclk-falling-edge: If present, sets receive clock phase to > > > + falling edge. > > > +- qca,sgmii-txclk-falling-edge: If present, sets transmit clock phase to > > > + falling edge. > > > > These are not something that other vendors may implement and therefore > > something we may want to make generic? Andrew? > > > > It was asked before whether this device uses source-synchronous clock > for SGMII or if it recovers the clock from the data stream. Just "pass" > was given for a response. > > https://patchwork.ozlabs.org/project/netdev/patch/8ddd76e484e1bedd12c87ea0810826b60e004a65.1591380105.git.noodles@earth.li/ > > One can, in principle, tell easily by examining schematics. If the SGMII > is only connected via RX_P, RX_N, TX_P, TX_N (and optionally there might > be external reference clocks for the SERDES lanes, but these are not > part of the data connection itself), then the clock is recovered from > the serial data stream, and we have no idea what "SGMII delays" are. > > If the schematic shows 2 extra clock signals, one in each transmit > direction, then this is, in Russell King's words, "a new world of RGMII > delay pain but for SGMII". In principle I would fully expect clock skews > to be necessary for any high-speed protocol with source-synchronous > clocking. The problem, really, is that we aren't ready to deal with this > properly. We aren't distinguishing "SGMII with clock" from "SGMII > without clock" in any way. We have no idea who else is using such a > thing. Depending on the magnitude of this new world, it may be wise to > let these bindings go in as-is, or do something more kernel-wide... I don't have the schematic for the device I've been working with, but the switch data sheet just shows 2 differential pairs (input/output) for the SerDes Interface (whereas the RGMII interfaces *are* listed with their clocks). J. -- I just Fedexed my soul to hell. I'm *real* clever.