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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0CC64C433EF for ; Tue, 8 Mar 2022 22:11:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243708AbiCHWML (ORCPT ); Tue, 8 Mar 2022 17:12:11 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45568 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229902AbiCHWML (ORCPT ); Tue, 8 Mar 2022 17:12:11 -0500 Received: from esa.microchip.iphmx.com (esa.microchip.iphmx.com [68.232.153.233]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7E43947AEA; Tue, 8 Mar 2022 14:11:13 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=microchip.com; i=@microchip.com; q=dns/txt; s=mchp; t=1646777473; x=1678313473; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=kQ5srqxv0waYBab8nwYT1ubD1rarswGHiGwSxhd9OF8=; b=etZFsZ2Wig4gasV5YZAuGDzJyrEZmJC0VvZ7qosJ+W8piWzJQGk5/F0x 3C9xmhSR2vcyZGu0x2TOnkiL7IbuwutMZAuPmevAsmkaduKlY/8JWriPW Q8M++YpWNDBtAWbfWW1tuFGXSPrU78nH8OGBPw9QfmZT0wLzdU8Uu+FEU 2/tK8btvGLuHd5CwggHjFsi7xAYjVTLL+n4OHSJo7+ryp3tqc6ANbP0vK QNAOJ4JPsbCd6rFmYMO9O9/7Vlr4JALhs4xV2THFY0USlHeePUKWOPVkJ XYeOklkK2/CPtgkYjQFJz9RZFrrAGwAEb42bRV4ilwF4FBf/idJihLiku w==; X-IronPort-AV: E=Sophos;i="5.90,165,1643698800"; d="scan'208";a="165010573" Received: from smtpout.microchip.com (HELO email.microchip.com) ([198.175.253.82]) by esa1.microchip.iphmx.com with ESMTP/TLS/AES256-SHA256; 08 Mar 2022 15:11:12 -0700 Received: from chn-vm-ex04.mchp-main.com (10.10.85.152) by chn-vm-ex04.mchp-main.com (10.10.85.152) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.17; Tue, 8 Mar 2022 15:11:11 -0700 Received: from localhost (10.10.115.15) by chn-vm-ex04.mchp-main.com (10.10.85.152) with Microsoft SMTP Server id 15.1.2375.17 via Frontend Transport; Tue, 8 Mar 2022 15:11:11 -0700 Date: Tue, 8 Mar 2022 23:14:04 +0100 From: Horatiu Vultur To: Andrew Lunn CC: , , , , , , , , , , , , Subject: Re: [PATCH net-next 2/3] dt-bindings: net: micrel: Configure latency values and timestamping check for LAN8814 phy Message-ID: <20220308221404.bwhujvsdp253t4g3@soft-dev3-1.localhost> References: <20220304093418.31645-1-Divya.Koppera@microchip.com> <20220304093418.31645-3-Divya.Koppera@microchip.com> <20220308154345.l4mk2oab4u5ydn5r@soft-dev3-1.localhost> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org The 03/08/2022 19:10, Andrew Lunn wrote: > > > > So this is a function of the track length between the MAC and the PHY? > > > > Nope. > > This latency represents the time it takes for the frame to travel from RJ45 > > module to the timestamping unit inside the PHY. To be more precisely, > > the timestamping unit will do the timestamp when it detects the end of > > the start of the frame. So it represents the time from when the frame > > reaches the RJ45 to when the end of start of the frame reaches the > > timestamping unit inside the PHY. > > I must be missing something here. How do you measure the latency > difference for a 1 meter cable vs a 100m cable? In the same way because the end result will be the same. Lets presume that the cable introduce a 5ns latency per meter. So, if we use a 1m cable and the mean path delay is 11, then the latency is 11 - 5. If we use a 100m cable then the mean path delay will be 506(if is not 506 then is something wrong) then the latency is 506 - 500. > Does 100m cable plus 1cm of track from the RJ45 to the PHY make a difference > compared to 100m cable plus 1.5cm of track? In that case I don't think you will see any difference. > Isn't this error all just in the noise? I am not sure I follow this question. > > Andrew -- /Horatiu