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[121.45.221.81]) by smtp.gmail.com with ESMTPSA id y142sm18158643pfc.53.2020.03.24.21.51.39 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 24 Mar 2020 21:51:43 -0700 (PDT) Subject: Re: [PATCH 1/2] dma-mapping: add a dma_ops_bypass flag to struct device To: Christoph Hellwig Cc: "Aneesh Kumar K.V" , iommu@lists.linux-foundation.org, linuxppc-dev@lists.ozlabs.org, Lu Baolu , Greg Kroah-Hartman , Joerg Roedel , Robin Murphy , linux-kernel@vger.kernel.org References: <20200320141640.366360-1-hch@lst.de> <20200320141640.366360-2-hch@lst.de> <2f31d0dd-aa7e-8b76-c8a1-5759fda5afc9@ozlabs.ru> <20200323083705.GA31245@lst.de> <20200323085059.GA32528@lst.de> <87sghz2ibh.fsf@linux.ibm.com> <20200323172256.GB31269@lst.de> <20200324075402.GJ23447@lst.de> From: Alexey Kardashevskiy Autocrypt: addr=aik@ozlabs.ru; keydata= mQINBE+rT0sBEADFEI2UtPRsLLvnRf+tI9nA8T91+jDK3NLkqV+2DKHkTGPP5qzDZpRSH6mD EePO1JqpVuIow/wGud9xaPA5uvuVgRS1q7RU8otD+7VLDFzPRiRE4Jfr2CW89Ox6BF+q5ZPV 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Zd44XWqUu7FzVOYaSgIvTP0hNrBYm/E6M7yrLbs3JY74fGzPWGRbBUHTZXQEqQnZglXaVB5V ZhSFtHopZnBSCUSNDbB+QGy4B/E++Bb02IBTGl/JxmOwG+kZUnymsPvTtnNIeTLHxN/H/ae0 c7E5M+/NpslPCmYnDjs5qg0/3ihh6XuOGggZQOqrYPC3PnsNs3NxirwOkVPQgO6mXxpuifvJ DG9EMkK8IBXnLulqVk54kf7fE0jT/d8RTtJIA92GzsgdK2rpT1MBKKVffjRFGwN7nQVOzi4T XrB5p+6ML7Bd84xOEGsj/vdaXmz1esuH7BOZAGEZfLRCHJ0GVCSssg== Message-ID: <41975da3-3a4a-fc3c-2b90-8d607cf220e6@ozlabs.ru> Date: Wed, 25 Mar 2020 15:51:36 +1100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200324075402.GJ23447@lst.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 24/03/2020 18:54, Christoph Hellwig wrote: > On Tue, Mar 24, 2020 at 02:05:54PM +1100, Alexey Kardashevskiy wrote: >> This is for persistent memory which you can DMA to/from but yet it does >> not appear in the system as a normal memory and therefore requires >> special handling anyway (O_DIRECT or DAX, I do not know the exact >> mechanics). All other devices in the system should just run as usual, >> i.e. use 1:1 mapping if possible. > > On other systems (x86 and arm) pmem as long as it is page backed does > not require any special handling. This must be some weird way powerpc > fucked up again, and I suspect you'll have to suffer from it. It does not matter if it is backed by pages or not, the problem may also appear if we wanted for example p2p PCI via IOMMU (between PHBs) and MMIO might be mapped way too high in the system address space and make 1:1 impossible. -- Alexey