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=-0.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 A4F6BC47404 for ; Mon, 7 Oct 2019 20:26:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6DEFC206C0 for ; Mon, 7 Oct 2019 20:26:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="OmUuP12g" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728702AbfJGUZ7 (ORCPT ); Mon, 7 Oct 2019 16:25:59 -0400 Received: from mail-wr1-f66.google.com ([209.85.221.66]:40367 "EHLO mail-wr1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728212AbfJGUZ7 (ORCPT ); Mon, 7 Oct 2019 16:25:59 -0400 Received: by mail-wr1-f66.google.com with SMTP id h4so8090091wrv.7 for ; Mon, 07 Oct 2019 13:25:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:from:date:message-id:subject:to; bh=j38m7Add2KbD5J4ODINJZZqe9yiJYPvqTx67RyFNngM=; b=OmUuP12ghIGPePIpfIea8N/KC9MdIOEcsF5hzsflWfQRAKkn4gtmB8F+iBLQL/W5Pj o6BpTCQIugBq764fFgNq2eylNoDrZhcXcW1A/GYNDwC9lSUBJMzgIHyMxBjMXc3coDmz JKcEktMHjwwxDUiaH84S1ojwUQqVVtUSuVmJxckm19jBjykPJ4wsHlHBybzgZVoeDCxd ic51O5OsFyr8qgr9ueOqXA5DYyuQTEzypg/5q3BRZTc8fXX3kQAHQbG+ZgJYQDp6syEF SS7/aNT9rMn/h/pWTeUpPeSz4ZVvoMQoryiCcP69VWokbnnPyZX1QbexK7iV0ThmLQVa 3uFg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:from:date:message-id:subject:to; bh=j38m7Add2KbD5J4ODINJZZqe9yiJYPvqTx67RyFNngM=; b=qGxu8ZBZcgp0M8GwKOJ1d6XPBBdFbymc5xKCILYLKaquCXZQhkgFtWwk7aZIHZUnIO iFzPGwCOMXgCX7MJc6NP/hCOsd8Cyalk5RwNPw5FL/WxVa5lUn52GBmDe45DRVnaZHot FjVMHushe6p1rpqyLxWPFUumDuo/njgRGeUP9qNN76tcaWdYgzbH1BkS6Mk71O2poZd7 NJ6SCuu04sbBG+0h63SDBUzECsCXsixmKeyeZOB+Q7EHyg09g5ZDV3CYAmPl9G5bM+Z2 6C/EAlOpP7NFENY32z65MwD9nS4Of0SfQr34S9oUgQLNrT3MHGcxOZJ2eeC3rb+KtQcS dbLw== X-Gm-Message-State: APjAAAUHIyY3c8hYYIewcttLEQ4FUV7MgkfYNHCqK3ymSS779pJyj6X7 dlK3al7Qqe27xJ7IK50LbJeXhAz1prE15drtnAWbtmmOuus= X-Google-Smtp-Source: APXvYqx1wwJ3WL4Mdk1PE5j/sXHlDnXgkxj97/5ydggGCxN5aH6xv9sdDS2EUFmlVRK1VOK5OJ52tj2vC52ZiY6ag0M= X-Received: by 2002:adf:97cb:: with SMTP id t11mr18129726wrb.312.1570479957034; Mon, 07 Oct 2019 13:25:57 -0700 (PDT) MIME-Version: 1.0 From: Guy Crazy Date: Mon, 7 Oct 2019 16:25:49 -0400 Message-ID: Subject: A Question about the patch "[PATCH v8 3/4] PCI: Introduce disable_acs_redir quirk" To: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, I have a question about this patch from the web link (https://lwn.net/ml/linux-kernel/20180730161840.13733-4-logang@deltatee.com/). According to the PCIe spec (PCIe 3.0), ACS Upstream Forwarding (UF) seems quite similar with Request Redirect (RR). Why pci_quirk_disable_intel_spt_pch_acs_redir in this patch seems disable RR but not UF? One related question in further: what's the difference between UF and RR (examples preferred)? Both seems redirect traffics originated from downstreams. Especially I feel confused about UF in the PCIe spec: PCIe switches must always route upstream requests towards RC because they target upstream destinations, why these switches need UF config? Thanks!