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=-2.0 required=3.0 tests=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 CC37CC3A5A0 for ; Mon, 19 Aug 2019 15:14:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9420E20651 for ; Mon, 19 Aug 2019 15:14:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=lunn.ch header.i=@lunn.ch header.b="ra7HSHHX" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727766AbfHSPOd (ORCPT ); Mon, 19 Aug 2019 11:14:33 -0400 Received: from vps0.lunn.ch ([185.16.172.187]:41928 "EHLO vps0.lunn.ch" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726628AbfHSPOd (ORCPT ); Mon, 19 Aug 2019 11:14:33 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lunn.ch; s=20171124; 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=nFZpbvfIabN6ZxKbSqt9D3Cc1DfWniWgSlpwjlw0n+Q=; b=ra7HSHHXFtGvuiSKMnz7YcpZjO qrgvxNKomvKX631ODd0yRNYN5vU+uCAPwJJSsQDQ0RYKuNOQG6e+VNA9mWEiAefB2ikestGWCLY0d fqPKtWdQSPhObn0N3cV3JQzPSc9ifLT00tRUuVJ/bn8YgTFmuAa3G/D+ERAvWik8IoHs=; Received: from andrew by vps0.lunn.ch with local (Exim 4.89) (envelope-from ) id 1hzjMb-0006xZ-Ad; Mon, 19 Aug 2019 17:14:29 +0200 Date: Mon, 19 Aug 2019 17:14:29 +0200 From: Andrew Lunn To: Vladimir Oltean Cc: Hubert Feurstein , netdev , lkml , Richard Cochran , Florian Fainelli , Heiner Kallweit , "David S. Miller" Subject: Re: [PATCH net-next 1/3] net: mdio: add support for passing a PTP system timestamp to the mii_bus driver Message-ID: <20190819151429.GG15291@lunn.ch> References: <20190816163157.25314-1-h.feurstein@gmail.com> <20190816163157.25314-2-h.feurstein@gmail.com> <20190819131736.GD8981@lunn.ch> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > > > How expensive is ptp_read_system_prets()? My original suggestion was > > > to unconditionally call it here, and then let the driver overwrite it > > > if it supports finer grained time stamping. MDIO is slow, so as long > > > as ptp_read_system_prets() is not too expensive, i prefer KISS. > > > > > > Andrew > > > > While that works for the pre_ts, it doesn't work for the post_ts (the > > MDIO bus core will unconditionally overwrite the system timestamp from > > the driver). > > Unless you're suggesting to keep the pre_ts unconditional and the > > post_ts under the "if" condition, which is a bit odd. > > According to my tests with a scope (measuring the width between SPI > > transfers with and without the ptp_read_system_*ts calls), two calls > > to ktime_get_real_ts64 amount to around 750 ns on a 1200 MHz Cortex A7 > > core, or around 90 clock cycles. > > 900 clock cycles, my bad. That is quite a lot. I was just expecting it to read a free running clock and maybe do some unit conversions. 900 cycles suggests it is doing a lot more. So please keep with the idea of the bus driver indicating if it supports the time stamping. But please make it a generic bus->flags, and bit 0 indicating time stamping. At some point in the future, it would be useful to indicate if the bus supports c45, which would be another use of flags. Thanks Andrew