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=-2.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,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 1A98BC32751 for ; Wed, 7 Aug 2019 12:38:19 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id E154721BF2 for ; Wed, 7 Aug 2019 12:38:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="kvd0yrCr" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E154721BF2 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=tIpi3v/5o4X8kOzDQmk6T9DgGTk4SxvOia+UUcVzpu0=; b=kvd0yrCrNP/yd9 8WJX5h5M3hxkK/x4qZsNHBRA6pz4pv0y+Oc3RdqaMWib2zbUbGNDTztHRshI0pGU/7QLR4hZrIp/7 /p3IjANQzEp5ioq23OHA6z7TXazv9+IwaQMlLhHMEytQgcqGfCDwUMSuE8obsimggkye/s8I4k0Nk q/v4ji/J+buhHZErlhK1rYMW1peyDfpgqPH0/A3C0V2EjNNAMUA1Hg9NwI0kJ2HiNdN8Z2U4b408B YkOrdx9ZFHdGwGTeF/fz3gYGXoXQqhjOp7tBHLy5lzxonMIaqs6qCTrCrzDkbhD6+Cs985FkQNc1V jX29cJdW5piIdnSrVCcg==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hvLCs-0000Gc-3f; Wed, 07 Aug 2019 12:38:18 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hvLCp-0000Fx-La for linux-arm-kernel@lists.infradead.org; Wed, 07 Aug 2019 12:38:16 +0000 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 3757F28; Wed, 7 Aug 2019 05:38:12 -0700 (PDT) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 358E03F575; Wed, 7 Aug 2019 05:38:10 -0700 (PDT) Date: Wed, 7 Aug 2019 13:38:08 +0100 From: Mark Rutland To: Rob Clark Subject: Re: [PATCH 1/2] drm: add cache support for arm64 Message-ID: <20190807123807.GD54191@lakrids.cambridge.arm.com> References: <20190805211451.20176-1-robdclark@gmail.com> <20190806084821.GA17129@lst.de> <20190806143457.GF475@lakrids.cambridge.arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.11.1+11 (2f07cb52) (2018-12-01) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190807_053815_752487_0D124768 X-CRM114-Status: GOOD ( 20.45 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Sean Paul , Maxime Ripard , Catalin Marinas , Maarten Lankhorst , LKML , dri-devel , David Airlie , Rob Clark , linux-arm-kernel@lists.infradead.org, Daniel Vetter , Greg Kroah-Hartman , Thomas Gleixner , Will Deacon , Christoph Hellwig , Allison Randal Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Aug 06, 2019 at 09:31:55AM -0700, Rob Clark wrote: > On Tue, Aug 6, 2019 at 7:35 AM Mark Rutland wrote: > > > > On Tue, Aug 06, 2019 at 07:11:41AM -0700, Rob Clark wrote: > > > On Tue, Aug 6, 2019 at 1:48 AM Christoph Hellwig wrote: > > > > > > > > This goes in the wrong direction. drm_cflush_* are a bad API we need to > > > > get rid of, not add use of it. The reason for that is two-fold: > > > > > > > > a) it doesn't address how cache maintaince actually works in most > > > > platforms. When talking about a cache we three fundamental operations: > > > > > > > > 1) write back - this writes the content of the cache back to the > > > > backing memory > > > > 2) invalidate - this remove the content of the cache > > > > 3) write back + invalidate - do both of the above > > > > > > Agreed that drm_cflush_* isn't a great API. In this particular case > > > (IIUC), I need wb+inv so that there aren't dirty cache lines that drop > > > out to memory later, and so that I don't get a cache hit on > > > uncached/wc mmap'ing. > > > > Is there a cacheable alias lying around (e.g. the linear map), or are > > these addresses only mapped uncached/wc? > > > > If there's a cacheable alias, performing an invalidate isn't sufficient, > > since a CPU can allocate a new (clean) entry at any point in time (e.g. > > as a result of prefetching or arbitrary speculation). > > I *believe* that there are not alias mappings (that I don't control > myself) for pages coming from > shmem_file_setup()/shmem_read_mapping_page().. AFAICT, that's regular anonymous memory, so there will be a cacheable alias in the linear/direct map. > digging around at what dma_sync_sg_* does under the hood, it looks > like it is just arch_sync_dma_for_cpu/device(), so I guess that should > be sufficient for what I need. I don't think that's the case, per the example I gave above. Thanks, Mark. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel