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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 104D4C433F5 for ; Fri, 3 Sep 2021 06:18:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DB6F6601FA for ; Fri, 3 Sep 2021 06:18:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230128AbhICGTS (ORCPT ); Fri, 3 Sep 2021 02:19:18 -0400 Received: from bmailout1.hostsharing.net ([83.223.95.100]:53149 "EHLO bmailout1.hostsharing.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234628AbhICGTR (ORCPT ); Fri, 3 Sep 2021 02:19:17 -0400 Received: from h08.hostsharing.net (h08.hostsharing.net [IPv6:2a01:37:1000::53df:5f1c:0]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "*.hostsharing.net", Issuer "RapidSSL TLS DV RSA Mixed SHA256 2020 CA-1" (verified OK)) by bmailout1.hostsharing.net (Postfix) with ESMTPS id AB73830027F59; Fri, 3 Sep 2021 08:18:14 +0200 (CEST) Received: by h08.hostsharing.net (Postfix, from userid 100393) id 9CB8F32415; Fri, 3 Sep 2021 08:18:14 +0200 (CEST) Date: Fri, 3 Sep 2021 08:18:14 +0200 From: Lukas Wunner To: Nathan Rossi Cc: linux-pci@vger.kernel.org, Nathan Rossi , Bjorn Helgaas Subject: Re: [PATCH] PCI: Add ACS errata for Pericom PI7C9X2G404 switch Message-ID: <20210903061814.GA15994@wunner.de> References: <20210903034029.306816-1-nathan@nathanrossi.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210903034029.306816-1-nathan@nathanrossi.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Fri, Sep 03, 2021 at 03:40:29AM +0000, Nathan Rossi wrote: > The Pericom PI7C9X2G404 PCIe switch has an errata for ACS P2P Request > Redirect behaviour when used in the cut-through forwarding mode. The > recommended work around for this issue is to use the switch in store and > forward mode. > > This change adds a fixup specific to this switch that when enabling the > downstream port it checks if it has enabled ACS P2P Request Redirect, > and if so changes the device (via the upstream port) to use the store > and forward operating mode. >From a quick look at the datasheet, this switch seems to support hot-plug on its Downstream Ports: https://www.diodes.com/assets/Datasheets/PI7C9X2G404SL.pdf I think your quirk isn't executed if a device is hotplugged to an initially-empty Downstream Port. Also, if a device which triggered the quirk is hot-removed and none of its siblings uses ACS P2P Request Redirect, cut-through forwarding isn't reinstated. Perhaps we need additional pci_fixup ELF sections which are used on hot-add and hot-remove? Thanks, Lukas