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=-5.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 4E31EC4338F for ; Fri, 13 Aug 2021 12:10:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 29C776109D for ; Fri, 13 Aug 2021 12:10:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240199AbhHMMK0 (ORCPT ); Fri, 13 Aug 2021 08:10:26 -0400 Received: from ni.piap.pl ([195.187.100.5]:53930 "EHLO ni.piap.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239977AbhHMMKY (ORCPT ); Fri, 13 Aug 2021 08:10:24 -0400 Received: from t19.piap.pl (OSB1819.piap.pl [10.0.9.19]) by ni.piap.pl (Postfix) with ESMTPSA id 82D2FC36953E; Fri, 13 Aug 2021 14:09:51 +0200 (CEST) DKIM-Filter: OpenDKIM Filter v2.11.0 ni.piap.pl 82D2FC36953E DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=piap.pl; s=mail; t=1628856591; bh=sb8e8PT14BLA3aZ+YBy/mSlODk/x4ypFarC/P08hpFM=; h=From:To:Cc:Subject:References:Date:In-Reply-To:From; b=Uve5ELBJeZgsyoJ2Ut+4X/C+QpRBdvI63X/vA04veCIK3dUhgW5oBz5lCL47VMBcN WX0GCobXQzVxcBEAnDArn/K40nlItSEKDWTFqMs3QbRQRm1+p5N25Pf84i7H8U3yuG YYjIhY/1OnDO69X0/EZdqHjVEiWaBF/zplryHGP8= From: =?utf-8?Q?Krzysztof_Ha=C5=82asa?= To: Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= Cc: Bjorn Helgaas , linux-pci@vger.kernel.org, Artem Lapkin , Neil Armstrong , Huacai Chen , Rob Herring , Lorenzo Pieralisi , Richard Zhu , Lucas Stach , linux-kernel@vger.kernel.org Subject: Re: [PATCH] PCIe: limit Max Read Request Size on i.MX to 512 bytes References: <20210813101305.GA598827@rocinante> Sender: khalasa@piap.pl Date: Fri, 13 Aug 2021 14:09:51 +0200 In-Reply-To: <20210813101305.GA598827@rocinante> ("Krzysztof =?utf-8?Q?Wil?= =?utf-8?Q?czy=C5=84ski=22's?= message of "Fri, 13 Aug 2021 12:13:05 +0200") Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-KLMS-Rule-ID: 1 X-KLMS-Message-Action: clean X-KLMS-AntiSpam-Lua-Profiles: 165559 [Aug 13 2021] X-KLMS-AntiSpam-Version: 5.9.20.0 X-KLMS-AntiSpam-Envelope-From: khalasa@piap.pl X-KLMS-AntiSpam-Rate: 0 X-KLMS-AntiSpam-Status: not_detected X-KLMS-AntiSpam-Method: none X-KLMS-AntiSpam-Auth: dkim=pass header.d=piap.pl X-KLMS-AntiSpam-Info: LuaCore: 454 454 39c6e442fd417993330528e7f9d13ac1bf7fdf8c, {Tracking_Text_ENG_RU_Has_Extended_Latin_Letters, eng}, {Tracking_marketers, three}, {Tracking_from_domain_doesnt_match_to}, d41d8cd98f00b204e9800998ecf8427e.com:7.1.1;piap.pl:7.1.1;127.0.0.199:7.1.2;t19.piap.pl:7.1.1 X-MS-Exchange-Organization-SCL: -1 X-KLMS-AntiSpam-Interceptor-Info: scan successful X-KLMS-AntiPhishing: Clean, bases: 2021/08/13 11:35:00 X-KLMS-AntiVirus: Kaspersky Security for Linux Mail Server, version 8.0.3.30, bases: 2021/08/13 05:50:00 #17026350 X-KLMS-AntiVirus-Status: Clean, skipped Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Krzysztof, :-) > Would it be possible to implement this particular MRRS fix as a quirk > only for the i.MX6 controller? Unless this is something that we need in > the core, a quirk would be preferred over something that changes the PCI > core. I have briefly considered it, but I think it would be *much* more complicated and error-prone. It also appears that there are more platforms which need it - the old CNS3xxx, which currently subverts the PCIE_BUS_PEER2PEER, the loongson, keystone, maybe all DWC PCIe. Multiplication of the "quirk" code doesn't really look good to me. TBH I don't think of this as of a "quirk" - all systems have MRRS limits, it just happens that these ones have their limit lower than 4096 bytes. This isn't a limitation of a particular PCIe device, this is a common limit of the whole system. Also I'm not exactly sure the loongson fixup is complete. It's only done at pci-enable*() time (e.g. for devices which have bigger MRRS after power-up), while e.g. the r8169 driver changes MRRS well after pci-enable*(). This means it needs to stay in/below pcie_get_readrq(), and while it could mean going to ops->write*, it would be a real mess parsing the devices, PCIE capabilities etc. Now it's basically a few lines in a seldom called routine in pci.c, and the loongson case (and others) can be made simpler (and really fixed) as well. --=20 Krzysztof "Chris" Ha=C5=82asa Sie=C4=87 Badawcza =C5=81ukasiewicz Przemys=C5=82owy Instytut Automatyki i Pomiar=C3=B3w PIAP Al. Jerozolimskie 202, 02-486 Warszawa