From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757285AbdKGPsm (ORCPT ); Tue, 7 Nov 2017 10:48:42 -0500 Received: from mail-it0-f47.google.com ([209.85.214.47]:55749 "EHLO mail-it0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753393AbdKGPsk (ORCPT ); Tue, 7 Nov 2017 10:48:40 -0500 X-Google-Smtp-Source: ABhQp+S9SCoY8nO+j3VIrYTaBcAO8VJERCiK00bF58cHmiLM0ybH+0XOUrLsZsidKmQ2kINbALlpRg== Date: Tue, 7 Nov 2017 08:48:38 -0700 From: Jason Gunthorpe To: "Wei Hu (Xavier)" Cc: Robin Murphy , Leon Romanovsky , shaobo.xu@intel.com, xavier.huwei@tom.com, lijun_nudt@163.com, oulijun@huawei.com, linux-rdma@vger.kernel.org, charles.chenxin@huawei.com, linuxarm@huawei.com, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, dledford@redhat.com, liuyixian@huawei.com, zhangxiping3@huawei.com, shaoboxu@tom.com Subject: Re: [PATCH for-next 2/4] RDMA/hns: Add IOMMU enable support in hip08 Message-ID: <20171107154838.GC21466@ziepe.ca> References: <1506763741-81429-1-git-send-email-xavier.huwei@huawei.com> <1506763741-81429-3-git-send-email-xavier.huwei@huawei.com> <20170930161023.GI2965@mtr-leonro.local> <59DF60A3.7080803@huawei.com> <5fe5f9b9-2c2b-ab3c-dafa-3e2add051bbb@arm.com> <59F97BBE.5070207@huawei.com> <5A011E49.6060407@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5A011E49.6060407@huawei.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 07, 2017 at 10:45:29AM +0800, Wei Hu (Xavier) wrote: > We reconstruct the code as below: > It replaces dma_alloc_coherent with __get_free_pages and > dma_map_single functions. So, we can vmap serveral ptrs returned by > __get_free_pages, right? Can't you just use vmalloc and dma_map that? Other drivers follow that approach.. However, dma_alloc_coherent and dma_map_single are not the same thing. You can't touch the vmap memory once you call dma_map unless the driver also includes dma cache flushing calls in all the right places. The difference is that alloc_coherent will return non-cachable memory if necessary, while get_free_pages does not. Jason