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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 656EBC31681 for ; Mon, 21 Jan 2019 17:55:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 413ED2084A for ; Mon, 21 Jan 2019 17:55:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727159AbfAURzR (ORCPT ); Mon, 21 Jan 2019 12:55:17 -0500 Received: from mail.netline.ch ([148.251.143.178]:36623 "EHLO netline-mail3.netline.ch" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726003AbfAURzR (ORCPT ); Mon, 21 Jan 2019 12:55:17 -0500 Received: from localhost (localhost [127.0.0.1]) by netline-mail3.netline.ch (Postfix) with ESMTP id 9FB932A6055; Mon, 21 Jan 2019 18:55:13 +0100 (CET) X-Virus-Scanned: Debian amavisd-new at netline-mail3.netline.ch Received: from netline-mail3.netline.ch ([127.0.0.1]) by localhost (netline-mail3.netline.ch [127.0.0.1]) (amavisd-new, port 10024) with LMTP id oDS3HFlYredT; Mon, 21 Jan 2019 18:55:13 +0100 (CET) Received: from thor (39.1.199.178.dynamic.wline.res.cust.swisscom.ch [178.199.1.39]) by netline-mail3.netline.ch (Postfix) with ESMTPSA id DFE7B2A6054; Mon, 21 Jan 2019 18:55:10 +0100 (CET) Received: from [::1] by thor with esmtp (Exim 4.92-RC4) (envelope-from ) id 1gldmv-0002S7-83; Mon, 21 Jan 2019 18:55:09 +0100 Subject: Re: [RFC PATCH] drm: disable WC optimization for cache coherent devices on non-x86 To: Ard Biesheuvel , Christoph Hellwig Cc: Will Deacon , David Zhou , Maxime Ripard , Benjamin Herrenschmidt , David Airlie , Maarten Lankhorst , Michel Daenzer , Linux Kernel Mailing List , amd-gfx@lists.freedesktop.org, Junwei Zhang , Huang Rui , dri-devel , Daniel Vetter , Michael Ellerman , Alex Deucher , Sean Paul , Christian Koenig , linux-arm-kernel References: <20190121100617.2311-1-ard.biesheuvel@linaro.org> <20190121150734.GA30582@infradead.org> <20190121155908.GA8084@infradead.org> <20190121162238.GA17651@infradead.org> From: =?UTF-8?Q?Michel_D=c3=a4nzer?= Openpgp: preference=signencrypt Autocrypt: addr=michel@daenzer.net; prefer-encrypt=mutual; keydata= mQGiBDsehS8RBACbsIQEX31aYSIuEKxEnEX82ezMR8z3LG8ktv1KjyNErUX9Pt7AUC7W3W0b LUhu8Le8S2va6hi7GfSAifl0ih3k6Bv1Itzgnd+7ZmSrvCN8yGJaHNQfAevAuEboIb+MaVHo 9EMJj4ikOcRZCmQWw7evu/D9uQdtkCnRY9iJiAGxbwCguBHtpoGMxDOINCr5UU6qt+m4O+UD /355ohBBzzyh49lTj0kTFKr0Ozd20G2FbcqHgfFL1dc1MPyigej2gLga2osu2QY0ObvAGkOu WBi3LTY8Zs8uqFGDC4ZAwMPoFy3yzu3ne6T7d/68rJil0QcdQjzzHi6ekqHuhst4a+/+D23h Za8MJBEcdOhRhsaDVGAJSFEQB1qLBACOs0xN+XblejO35gsDSVVk8s+FUUw3TSWJBfZa3Imp V2U2tBO4qck+wqbHNfdnU/crrsHahjzBjvk8Up7VoY8oT+z03sal2vXEonS279xN2B92Tttr AgwosujguFO/7tvzymWC76rDEwue8TsADE11ErjwaBTs8ZXfnN/uAANgPLQjTWljaGVsIERh ZW56ZXIgPG1pY2hlbEBkYWVuemVyLm5ldD6IXgQTEQIAHgUCQFXxJgIbAwYLCQgHAwIDFQID AxYCAQIeAQIXgAAKCRBaga+OatuyAIrPAJ9ykonXI3oQcX83N2qzCEStLNW47gCeLWm/QiPY jqtGUnnSbyuTQfIySkK5AQ0EOx6FRRAEAJZkcvklPwJCgNiw37p0GShKmFGGqf/a3xZZEpjI qNxzshFRFneZze4f5LhzbX1/vIm5+ZXsEWympJfZzyCmYPw86QcFxyZflkAxHx9LeD+89Elx bw6wT0CcLvSv8ROfU1m8YhGbV6g2zWyLD0/naQGVb8e4FhVKGNY2EEbHgFBrAAMGA/0VktFO CxFBdzLQ17RCTwCJ3xpyP4qsLJH0yCoA26rH2zE2RzByhrTFTYZzbFEid3ddGiHOBEL+bO+2 GNtfiYKmbTkj1tMZJ8L6huKONaVrASFzLvZa2dlc2zja9ZSksKmge5BOTKWgbyepEc5qxSju YsYrX5xfLgTZC5abhhztpYhGBBgRAgAGBQI7HoVFAAoJEFqBr45q27IAlscAn2Ufk2d6/3p4 Cuyz/NX7KpL2dQ8WAJ9UD5JEakhfofed8PSqOM7jOO3LCA== Message-ID: <59ccf85d-b99d-b5c8-ea87-66c2a892e197@daenzer.net> Date: Mon, 21 Jan 2019 18:55:08 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-CA Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019-01-21 5:30 p.m., Ard Biesheuvel wrote: > On Mon, 21 Jan 2019 at 17:22, Christoph Hellwig wrote: > >> Until that happens we should just change the driver ifdefs to default >> the hacks to off and only enable them on setups where we 100% >> positively know that they actually work. And document that fact >> in big fat comments. > > Well, as I mentioned in my commit log as well, if we default to off > unless CONFIG_X86, we may break working setups on MIPS and Power where > the device is in fact non-cache coherent, and relies on this > 'optimization' to get things working. FWIW, the amdgpu driver doesn't rely on non-snooped transfers for correct basic operation (the scenario Christian brought up is a very specialized use-case), so that shouldn't be an issue. -- Earthling Michel Dänzer | http://www.amd.com Libre software enthusiast | Mesa and X developer