From patchwork Sun Jun 14 20:54:09 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Vladimir Oltean X-Patchwork-Id: 217775 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=-9.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, USER_AGENT_GIT autolearn=ham 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 527D0C433DF for ; Sun, 14 Jun 2020 20:57:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3114C2071A for ; Sun, 14 Jun 2020 20:57:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="TSwpfReS" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727817AbgFNUyZ (ORCPT ); Sun, 14 Jun 2020 16:54:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45466 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726648AbgFNUyY (ORCPT ); Sun, 14 Jun 2020 16:54:24 -0400 Received: from mail-ej1-x641.google.com (mail-ej1-x641.google.com [IPv6:2a00:1450:4864:20::641]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BE272C03E97C; Sun, 14 Jun 2020 13:54:23 -0700 (PDT) Received: by mail-ej1-x641.google.com with SMTP id n24so15297735ejd.0; Sun, 14 Jun 2020 13:54:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=tgWmDiNQdaMJHDiSYz9iwVWHmMa2MnorA3k8D09lAhw=; b=TSwpfReSaIF4z1dNW/MPfEH3d2mft/xewUwQlCZbnZjgyZu2sBMlSOBs4QcfXnZ1Ph 60QXSBdL9Ju0/27De+oMUYYOYJmZOAhh3QNSh1wDIB90fO5rHzzTpTE8aRSRZvU9KQTc XmJXHTSnu4qw05ma9uzOM7zTSHKLltzorWEMaXGKhdU2jTvsDtki9QAFoOYkme5Ne6Ko aN3Z7sVGrRZvegdQNELrBy8H1pI+cnM7GZ3byYbIhOkBYuWIZUa1vsavYcxcrJf0DDv7 HYtHyfCVwPDrdxXFORYuBVVql4ygjGTqmavC19ycUkZtZ8DVt6rFiyDYDdh0lKMbiyhi Oyaw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=tgWmDiNQdaMJHDiSYz9iwVWHmMa2MnorA3k8D09lAhw=; b=GQAaqQI/mRhJD8mkX4jTklD3IeThG/+vVP359xigg9ESHattJobZ3S1WOdkLpBspz4 nALoKmfUHg50qU8om9sXkkNNrM6RexfQH44CuCHL2wQK5mGjhYA+s+Jk5RngSufQqgV7 geE+c7cpa23oLVVpL3WAgUPhPSAUYPmOoxGOTMLAWFwU9h0JSxBxVw1XkXjq/Ge7cK1F tkA0pDAEMFOoDs3JQIcFgJ7J1tjjHXVtVsvo0Euv/FIwSCcdu9JM8Sfl1sHKwdnn2Lnq 7mL8vP6Tx3ZvMFRthebaFniUmgyKRUcSZK5aA+f6ZM2pXAcI7H4j13+Wk8RmTfWNcw+r 0uKQ== X-Gm-Message-State: AOAM5323cYkHBPqnaU+j+BZsCjsnkGjFyPZqvxfTOeArGZKWXeAxa/Z4 t8ufzXwafI30zMGRxZheh8f7DCCY X-Google-Smtp-Source: ABdhPJyI0Ife0VA9liuc0IpiUy/Ri6tXkbWcxLylTVYh28H70Dv6sZoyf+UiqjfyGF5+uIVa1ctLqA== X-Received: by 2002:a17:906:fc13:: with SMTP id ov19mr22331139ejb.212.1592168062154; Sun, 14 Jun 2020 13:54:22 -0700 (PDT) Received: from localhost.localdomain ([188.26.56.128]) by smtp.gmail.com with ESMTPSA id m23sm7108163edr.86.2020.06.14.13.54.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 14 Jun 2020 13:54:21 -0700 (PDT) From: Vladimir Oltean To: f.fainelli@gmail.com, vivien.didelot@gmail.com, andrew@lunn.ch, davem@davemloft.net Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, richardcochran@gmail.com, vinicius.gomes@intel.com Subject: [PATCH net] net: dsa: sja1105: fix PTP timestamping with large tc-taprio cycles Date: Sun, 14 Jun 2020 23:54:09 +0300 Message-Id: <20200614205409.1580736-1-olteanv@gmail.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org From: Vladimir Oltean It isn't actually described clearly at all in UM10944.pdf, but on TX of a management frame (such as PTP), this needs to happen: - The destination MAC address (i.e. 01-80-c2-00-00-0e), along with the desired destination port, need to be installed in one of the 4 management slots of the switch, over SPI. - The host can poll over SPI for that management slot's ENFPORT field. That gets unset when the switch has matched the slot to the frame. And therein lies the problem. ENFPORT does not mean that the packet has been transmitted. Just that it has been received over the CPU port, and that the mgmt slot is yet again available. This is relevant because of what we are doing in sja1105_ptp_txtstamp_skb, which is called right after sja1105_mgmt_xmit. We are in a hard real-time deadline, since the hardware only gives us 24 bits of TX timestamp, so we need to read the full PTP clock to reconstruct it. Because we're in a hurry (in an attempt to make sure that we have a full 64-bit PTP time which is as close as possible to the actual transmission time of the frame, to avoid 24-bit wraparounds), first we read the PTP clock, then we poll for the TX timestamp to become available. But of course, we don't know for sure that the frame has been transmitted when we read the full PTP clock. We had assumed that ENFPORT means it has, but the assumption is incorrect. And while in most real-life scenarios this has never been caught due to software delays, nowhere is this fact more obvious than with a tc-taprio offload, where PTP traffic gets a small timeslot very rarely (example: 1 packet per 10 ms). In that case, we will be reading the PTP clock for timestamp reconstruction too early (before the packet has been transmitted), and this renders the reconstruction procedure incorrect (see the assumptions described in the comments found on function sja1105_tstamp_reconstruct). So the PTP TX timestamps will be off by 1<<24 clock ticks, or 135 ms (1 tick is 8 ns). So fix this case of premature optimization by simply reordering the sja1105_ptpegr_ts_poll and the sja1105_ptpclkval_read function calls. It turns out that in practice, the 135 ms hard deadline for PTP timestamp wraparound is not so hard, since even the most bandwidth-intensive PTP profiles, such as 802.1AS-2011, have a sync frame interval of 125 ms. So if we couldn't deliver a timestamp in 135 ms (which we can), we're toast and have much bigger problems anyway. Fixes: 47ed985e97f5 ("net: dsa: sja1105: Add logic for TX timestamping") Signed-off-by: Vladimir Oltean --- drivers/net/dsa/sja1105/sja1105_ptp.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/drivers/net/dsa/sja1105/sja1105_ptp.c b/drivers/net/dsa/sja1105/sja1105_ptp.c index bc0e47c1dbb9..177134596458 100644 --- a/drivers/net/dsa/sja1105/sja1105_ptp.c +++ b/drivers/net/dsa/sja1105/sja1105_ptp.c @@ -891,16 +891,16 @@ void sja1105_ptp_txtstamp_skb(struct dsa_switch *ds, int port, mutex_lock(&ptp_data->lock); - rc = sja1105_ptpclkval_read(priv, &ticks, NULL); + rc = sja1105_ptpegr_ts_poll(ds, port, &ts); if (rc < 0) { - dev_err(ds->dev, "Failed to read PTP clock: %d\n", rc); + dev_err(ds->dev, "timed out polling for tstamp\n"); kfree_skb(skb); goto out; } - rc = sja1105_ptpegr_ts_poll(ds, port, &ts); + rc = sja1105_ptpclkval_read(priv, &ticks, NULL); if (rc < 0) { - dev_err(ds->dev, "timed out polling for tstamp\n"); + dev_err(ds->dev, "Failed to read PTP clock: %d\n", rc); kfree_skb(skb); goto out; }