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=-2.2 required=3.0 tests=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 5C470C3A59D for ; Fri, 16 Aug 2019 19:44:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3B5C2206C1 for ; Fri, 16 Aug 2019 19:44:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728018AbfHPToC (ORCPT ); Fri, 16 Aug 2019 15:44:02 -0400 Received: from foss.arm.com ([217.140.110.172]:60504 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727701AbfHPTn6 (ORCPT ); Fri, 16 Aug 2019 15:43:58 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A4B8428; Fri, 16 Aug 2019 12:43:57 -0700 (PDT) Received: from [10.1.197.57] (e110467-lin.cambridge.arm.com [10.1.197.57]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 60F9C3F706; Fri, 16 Aug 2019 12:43:55 -0700 (PDT) Subject: Re: [Freedreno] [PATCH v3 0/2] iommu/arm-smmu: Split pagetable support To: Rob Clark , Jordan Crouse Cc: freedreno , Rob Herring , Will Deacon , Jean-Philippe Brucker , linux-arm-msm , Joerg Roedel , Linux Kernel Mailing List , "list@263.net:IOMMU DRIVERS" , Joerg Roedel , iommu@lists.linux-foundation.org, Zhen Lei , "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" References: <1565216500-28506-1-git-send-email-jcrouse@codeaurora.org> <20190815153304.GD28465@jcrouse1-lnx.qualcomm.com> From: Robin Murphy Message-ID: <3ea2755f-6d4d-736d-bebd-455a7967e381@arm.com> Date: Fri, 16 Aug 2019 20:43:53 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 16/08/2019 19:12, Rob Clark wrote: > On Fri, Aug 16, 2019 at 9:58 AM Robin Murphy wrote: >> >> Hi Jordan, >> >> On 15/08/2019 16:33, Jordan Crouse wrote: >>> On Wed, Aug 07, 2019 at 04:21:38PM -0600, Jordan Crouse wrote: >>>> (Sigh, resend. I freaked out my SMTP server) >>>> >>>> This is part of an ongoing evolution for enabling split pagetable support for >>>> arm-smmu. Previous versions can be found [1]. >>>> >>>> In the discussion for v2 Robin pointed out that this is a very Adreno specific >>>> use case and that is exactly true. Not only do we want to configure and use a >>>> pagetable in the TTBR1 space, we also want to configure the TTBR0 region but >>>> not allocate a pagetable for it or touch it until the GPU hardware does so. As >>>> much as I want it to be a generic concept it really isn't. >>>> >>>> This revision leans into that idea. Most of the same io-pgtable code is there >>>> but now it is wrapped as an Adreno GPU specific format that is selected by the >>>> compatible string in the arm-smmu device. >>>> >>>> Additionally, per Robin's suggestion we are skipping creating a TTBR0 pagetable >>>> to save on wasted memory. >>>> >>>> This isn't as clean as I would like it to be but I think that this is a better >>>> direction than trying to pretend that the generic format would work. >>>> >>>> I'm tempting fate by posting this and then taking some time off, but I wanted >>>> to try to kick off a conversation or at least get some flames so I can try to >>>> refine this again next week. Please take a look and give some advice on the >>>> direction. >>> >>> Will, Robin - >>> >>> Modulo the impl changes from Robin, do you think that using a dedicated >>> pagetable format is the right approach for supporting split pagetables for the >>> Adreno GPU? >> >> How many different Adreno drivers would benefit from sharing it? > > Hypothetically everything back to a3xx, so I *could* see usefulness of > this in qcom_iommu (or maybe even msm-iommu). OTOH maybe with > "modularizing" arm-smmu we could re-combine qcom_iommu and arm-smmu. Indeed, that's certainly something I'm planning to investigate as a future refactoring step. > And as a practical matter, I'm not sure if anyone will get around to > backporting per-context pagetables as far back as a3xx. > > BR, > -R > >> The more I come back to this, the more I'm convinced that io-pgtable >> should focus on the heavy lifting of pagetable management - the code >> that nobody wants to have to write at all, let alone more than once - >> and any subtleties which aren't essential to that should be pushed back >> into whichever callers actually care. Consider that already, literally >> no caller actually uses an unmodified stage 1 TCR value as provided in >> the io_pgtable_cfg. >> >> I feel it would be most productive to elaborate further in the form of >> patches, so let me get right on that and try to bash something out >> before I go home tonight... ...and now there's a rough WIP branch here: http://linux-arm.org/git?p=linux-rm.git;a=shortlog;h=refs/heads/iommu/pgtable I'll finish testing and polishing those patches at some point next week, probably, but hopefully they're sufficiently illustrative for the moment. Robin.