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 5B5B0C7618B for ; Wed, 24 Jul 2019 13:51:30 +0000 (UTC) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org [140.211.169.12]) (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 3647E217D4 for ; Wed, 24 Jul 2019 13:51:30 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3647E217D4 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from mail.linux-foundation.org (localhost [127.0.0.1]) by mail.linuxfoundation.org (Postfix) with ESMTP id 09B96E63; Wed, 24 Jul 2019 13:51:30 +0000 (UTC) Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 02D54E41 for ; Wed, 24 Jul 2019 13:51:29 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp1.linuxfoundation.org (Postfix) with ESMTP id 79142FE for ; Wed, 24 Jul 2019 13:51:28 +0000 (UTC) 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 21F7B28; Wed, 24 Jul 2019 06:51:28 -0700 (PDT) Received: from arrakis.emea.arm.com (arrakis.cambridge.arm.com [10.1.196.78]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 7116C3F71A; Wed, 24 Jul 2019 06:51:26 -0700 (PDT) Date: Wed, 24 Jul 2019 14:51:24 +0100 From: Catalin Marinas To: Nicolas Saenz Julienne Subject: Re: [RFC 3/4] dma-direct: add dma_direct_min_mask Message-ID: <20190724135124.GA44864@arrakis.emea.arm.com> References: <20190717153135.15507-1-nsaenzjulienne@suse.de> <20190717153135.15507-4-nsaenzjulienne@suse.de> <20190718091526.GA25321@lst.de> <13dd1a4f33fcf814545f0d93f18429e853de9eaf.camel@suse.de> <58753252bd7964e3b9e9558b633bd325c4a898a1.camel@suse.de> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <58753252bd7964e3b9e9558b633bd325c4a898a1.camel@suse.de> User-Agent: Mutt/1.10.1 (2018-07-13) Cc: stefan.wahren@i2se.com, f.fainelli@gmail.com, Robin Murphy , phil@raspberrypi.org, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, Jisheng.Zhang@synaptics.com, mbrugger@suse.com, will@kernel.org, Christoph Hellwig , linux-arm-kernel@lists.infradead.org X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: iommu-bounces@lists.linux-foundation.org Errors-To: iommu-bounces@lists.linux-foundation.org On Fri, Jul 19, 2019 at 03:08:52PM +0200, Nicolas Saenz Julienne wrote: > On Thu, 2019-07-18 at 13:18 +0200, Nicolas Saenz Julienne wrote: > > On Thu, 2019-07-18 at 11:15 +0200, Christoph Hellwig wrote: > > > On Wed, Jul 17, 2019 at 05:31:34PM +0200, Nicolas Saenz Julienne wrote: > > > > Historically devices with ZONE_DMA32 have been assumed to be able to > > > > address at least the lower 4GB of ram for DMA. This is still the defualt > > > > behavior yet the Raspberry Pi 4 is limited to the first GB of memory. > > > > This has been observed to trigger failures in dma_direct_supported() as > > > > the 'min_mask' isn't properly set. > > > > > > > > We create 'dma_direct_min_mask' in order for the arch init code to be > > > > able to fine-tune dma direct's 'min_dma' mask. > > > > > > Normally we use ZONE_DMA for that case. > > > > Fair enough, I didn't think of that possibility. > > > > So would the arm64 maintainers be happy with something like this: > > > > - ZONE_DMA: Follows standard definition, 16MB in size. ARCH_ZONE_DMA_BITS is > > left as is. > > - ZONE_DMA32: Will honor the most constraining 'dma-ranges'. Which so far for > > most devices is 4G, except for RPi4. > > - ZONE_NORMAL: The rest of the memory. > > Never mind this suggestion, I don't think it makes any sense. If anything arm64 > seems to fit the ZONE_DMA usage pattern of arm and powerpc: where ZONE_DMA's > size is decided based on ram size and/or board configuration. It was actually > set-up like this until Christoph's ad67f5a6545f7 ("arm64: replace ZONE_DMA with > ZONE_DMA32"). > > So the easy solution would be to simply revert that commit. On one hand I feel > it would be a step backwards as most 64 bit architectures have been moving to > use ZONE_DMA32. On the other, current ZONE_DMA32 usage seems to be heavily > rooted on having a 32 bit DMA mask*, which will no longer be the case on arm64 > if we want to support the RPi 4. > > So the way I see it and lacking a better solution, the argument is stronger on > moving back arm64 to using ZONE_DMA. Any comments/opinions? As it was suggested in this or the previous thread, I'm not keen on limiting ZONE_DMA32 to the smalles RPi4 can cover, as the naming implies this zone should cover 32-bit devices that can deal with a full 32-bit mask. I think it may be better if we have both ZONE_DMA and ZONE_DMA32 on arm64. ZONE_DMA would be based on the smallest dma-ranges as described in the DT while DMA32 covers the first naturally aligned 4GB of RAM (unchanged). When a smaller ZONE_DMA is not needed, it could be expanded to cover what would normally be ZONE_DMA32 (or could we have ZONE_DMA as 0-bytes? I don't think GFP_DMA can still allocate memory in this case). We'd probably have to define ARCH_ZONE_DMA_BITS for arm64 to something smaller than 32-bit but sufficient to cover the known platforms like RPi4 (the current 24 is too small, so maybe 30). AFAICT, __dma_direct_optimal_gfp_mask() figures out whether GFP_DMA or GFP_DMA32 should be passed. -- Catalin _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu