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=-3.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,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 544F6C4338F for ; Mon, 9 Aug 2021 17:48:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3363460F56 for ; Mon, 9 Aug 2021 17:48:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234723AbhHIRsp (ORCPT ); Mon, 9 Aug 2021 13:48:45 -0400 Received: from so254-9.mailgun.net ([198.61.254.9]:10974 "EHLO so254-9.mailgun.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234745AbhHIRsl (ORCPT ); Mon, 9 Aug 2021 13:48:41 -0400 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1628531295; h=Message-ID: References: In-Reply-To: Subject: Cc: To: From: Date: Content-Transfer-Encoding: Content-Type: MIME-Version: Sender; bh=8guuvupjL6NqII3stb55gN3OwOOwh2DbzAjTfValqJY=; b=FiuKgcQII/ydK0gv8qAIKBfKpDq8LvMC/5opqclIFfOHuEmfW3nxqqGfKnkoFjpZji5eAimI T6LqbLNQam9f6TjeFY8gbh1y0lsB0Fv+F9VIKeJOrkPMFLZcAzyjqd6PJj/HCBH+58oaUtqY co3yr7EQ28YzV2C3smImq8xWtnw= X-Mailgun-Sending-Ip: 198.61.254.9 X-Mailgun-Sid: WyI0MWYwYSIsICJsaW51eC1rZXJuZWxAdmdlci5rZXJuZWwub3JnIiwgImJlOWU0YSJd Received: from smtp.codeaurora.org (ec2-35-166-182-171.us-west-2.compute.amazonaws.com [35.166.182.171]) by smtp-out-n07.prod.us-east-1.postgun.com with SMTP id 61116a3fb3873958f5f1c3ad (version=TLS1.2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256); Mon, 09 Aug 2021 17:47:43 GMT Sender: saiprakash.ranjan=codeaurora.org@mg.codeaurora.org Received: by smtp.codeaurora.org (Postfix, from userid 1001) id 22C33C43149; Mon, 9 Aug 2021 17:47:42 +0000 (UTC) Received: from mail.codeaurora.org (localhost.localdomain [127.0.0.1]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) (Authenticated sender: saiprakash.ranjan) by smtp.codeaurora.org (Postfix) with ESMTPSA id 33FD9C433F1; Mon, 9 Aug 2021 17:47:40 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Mon, 09 Aug 2021 23:17:40 +0530 From: Sai Prakash Ranjan To: Will Deacon , Rob Clark Cc: Georgi Djakov , "Isaac J. Manjarres" , David Airlie , Akhil P Oommen , "list@263.net:IOMMU DRIVERS , Joerg Roedel ," , Linux Kernel Mailing List , Sean Paul , Jordan Crouse , Kristian H Kristensen , dri-devel , Daniel Vetter , linux-arm-msm , freedreno , Robin Murphy , "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" Subject: Re: [Freedreno] [PATCH 0/3] iommu/drm/msm: Allow non-coherent masters to use system cache In-Reply-To: <20210809174022.GA1840@willie-the-truck> References: <20210728140052.GB22887@mms-0441> <8b2742c8891abe4fec3664730717a089@codeaurora.org> <20210802105544.GA27657@willie-the-truck> <20210802151409.GE28735@willie-the-truck> <20210809145651.GC1458@willie-the-truck> <20210809170508.GB1589@willie-the-truck> <20210809174022.GA1840@willie-the-truck> Message-ID: <76bfd0b4248148dfbf9d174ddcb4c2a2@codeaurora.org> X-Sender: saiprakash.ranjan@codeaurora.org User-Agent: Roundcube Webmail/1.3.9 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021-08-09 23:10, Will Deacon wrote: > On Mon, Aug 09, 2021 at 10:18:21AM -0700, Rob Clark wrote: >> On Mon, Aug 9, 2021 at 10:05 AM Will Deacon wrote: >> > >> > On Mon, Aug 09, 2021 at 09:57:08AM -0700, Rob Clark wrote: >> > > On Mon, Aug 9, 2021 at 7:56 AM Will Deacon wrote: >> > > > On Mon, Aug 02, 2021 at 06:36:04PM -0700, Rob Clark wrote: >> > > > > On Mon, Aug 2, 2021 at 8:14 AM Will Deacon wrote: >> > > > > > On Mon, Aug 02, 2021 at 08:08:07AM -0700, Rob Clark wrote: >> > > > > > > On Mon, Aug 2, 2021 at 3:55 AM Will Deacon wrote: >> > > > > > > > On Thu, Jul 29, 2021 at 10:08:22AM +0530, Sai Prakash Ranjan wrote: >> > > > > > > > > On 2021-07-28 19:30, Georgi Djakov wrote: >> > > > > > > > > > On Mon, Jan 11, 2021 at 07:45:02PM +0530, Sai Prakash Ranjan wrote: >> > > > > > > > > > > commit ecd7274fb4cd ("iommu: Remove unused IOMMU_SYS_CACHE_ONLY flag") >> > > > > > > > > > > removed unused IOMMU_SYS_CACHE_ONLY prot flag and along with it went >> > > > > > > > > > > the memory type setting required for the non-coherent masters to use >> > > > > > > > > > > system cache. Now that system cache support for GPU is added, we will >> > > > > > > > > > > need to set the right PTE attribute for GPU buffers to be sys cached. >> > > > > > > > > > > Without this, the system cache lines are not allocated for GPU. >> > > > > > > > > > > >> > > > > > > > > > > So the patches in this series introduces a new prot flag IOMMU_LLC, >> > > > > > > > > > > renames IO_PGTABLE_QUIRK_ARM_OUTER_WBWA to IO_PGTABLE_QUIRK_PTW_LLC >> > > > > > > > > > > and makes GPU the user of this protection flag. >> > > > > > > > > > >> > > > > > > > > > Thank you for the patchset! Are you planning to refresh it, as it does >> > > > > > > > > > not apply anymore? >> > > > > > > > > > >> > > > > > > > > >> > > > > > > > > I was waiting on Will's reply [1]. If there are no changes needed, then >> > > > > > > > > I can repost the patch. >> > > > > > > > >> > > > > > > > I still think you need to handle the mismatched alias, no? You're adding >> > > > > > > > a new memory type to the SMMU which doesn't exist on the CPU side. That >> > > > > > > > can't be right. >> > > > > > > > >> > > > > > > >> > > > > > > Just curious, and maybe this is a dumb question, but what is your >> > > > > > > concern about mismatched aliases? I mean the cache hierarchy on the >> > > > > > > GPU device side (anything beyond the LLC) is pretty different and >> > > > > > > doesn't really care about the smmu pgtable attributes.. >> > > > > > >> > > > > > If the CPU accesses a shared buffer with different attributes to those which >> > > > > > the device is using then you fall into the "mismatched memory attributes" >> > > > > > part of the Arm architecture. It's reasonably unforgiving (you should go and >> > > > > > read it) and in some cases can apply to speculative accesses as well, but >> > > > > > the end result is typically loss of coherency. >> > > > > >> > > > > Ok, I might have a few other sections to read first to decipher the >> > > > > terminology.. >> > > > > >> > > > > But my understanding of LLC is that it looks just like system memory >> > > > > to the CPU and GPU (I think that would make it "the point of >> > > > > coherence" between the GPU and CPU?) If that is true, shouldn't it be >> > > > > invisible from the point of view of different CPU mapping options? >> > > > >> > > > You could certainly build a system where mismatched attributes don't cause >> > > > loss of coherence, but as it's not guaranteed by the architecture and the >> > > > changes proposed here affect APIs which are exposed across SoCs, then I >> > > > don't think it helps much. >> > > > >> > > >> > > Hmm, the description of the new mapping flag is that it applies only >> > > to transparent outer level cache: >> > > >> > > +/* >> > > + * Non-coherent masters can use this page protection flag to set cacheable >> > > + * memory attributes for only a transparent outer level of cache, also known as >> > > + * the last-level or system cache. >> > > + */ >> > > +#define IOMMU_LLC (1 << 6) >> > > >> > > But I suppose we could call it instead IOMMU_QCOM_LLC or something >> > > like that to make it more clear that it is not necessarily something >> > > that would work with a different outer level cache implementation? >> > >> > ... or we could just deal with the problem so that other people can reuse >> > the code. I haven't really understood the reluctance to solve this properly. >> > >> > Am I missing some reason this isn't solvable? >> >> Oh, was there another way to solve it (other than foregoing setting >> INC_OCACHE in the pgtables)? Maybe I misunderstood, is there a >> corresponding setting on the MMU pgtables side of things? > > Right -- we just need to program the CPU's MMU with the matching memory > attributes! It's a bit more fiddly if you're just using ioremap_wc() > though, as it's usually the DMA API which handles the attributes under > the > hood. > > Anyway, sorry, I should've said that explicitly earlier on. We've done > this > sort of thing in the Android tree so I assumed Sai knew what needed to > be > done and then I didn't think to explain to you :( > Right I was aware of that but even in the android tree there is no user :) I think we can't have a new memory type without any user right in upstream like android tree? @Rob, I think you already tried adding a new MT and used pgprot_syscached() in GPU driver but it was crashing? Thanks, Sai -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation