Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753823Ab2JPKhT (ORCPT ); Tue, 16 Oct 2012 06:37:19 -0400 Received: from caramon.arm.linux.org.uk ([78.32.30.218]:53191 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752567Ab2JPKhR (ORCPT ); Tue, 16 Oct 2012 06:37:17 -0400 Date: Tue, 16 Oct 2012 11:37:02 +0100 From: Russell King - ARM Linux To: Hiroshi Doyu Cc: "m.szyprowski@samsung.com" , "inki.dae@samsung.com" , "arnd@arndb.de" , "linux-kernel@vger.kernel.org" , "linaro-mm-sig@lists.linaro.org" , "linux-mm@kvack.org" , "kyungmin.park@samsung.com" , "linux-arm-kernel@lists.infradead.org" , "linux-tegra@vger.kernel.org" Subject: Re: [Linaro-mm-sig] [RFC 0/2] DMA-mapping & IOMMU - physically contiguous allocations Message-ID: <20121016103702.GB21164@n2100.arm.linux.org.uk> References: <20121016090434.7d5e088152a3e0b0606903c8@nvidia.com> <20121016085928.GV21164@n2100.arm.linux.org.uk> <20121016.132755.661591248175727826.hdoyu@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20121016.132755.661591248175727826.hdoyu@nvidia.com> User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2103 Lines: 49 On Tue, Oct 16, 2012 at 12:27:55PM +0200, Hiroshi Doyu wrote: > Hi Russell, > > Russell King - ARM Linux wrote @ Tue, 16 Oct 2012 10:59:28 +0200: > > > On Tue, Oct 16, 2012 at 09:04:34AM +0300, Hiroshi Doyu wrote: > > > In addition to those contiguous/discontiguous page allocation, is > > > there any way to _import_ anonymous pages allocated by a process to be > > > used in dma-mapping API later? > > > > > > I'm considering the following scenario, an user process allocates a > > > buffer by malloc() in advance, and then it asks some driver to convert > > > that buffer into IOMMU'able/DMA'able ones later. In this case, pages > > > are discouguous and even they may not be yet allocated at > > > malloc()/mmap(). > > > > That situation is covered. It's the streaming API you're wanting for that. > > dma_map_sg() - but you may need additional cache handling via > > flush_dcache_page() to ensure that your code is safe for all CPU cache > > architectures. > > > > Remember that pages allocated into userspace will be cacheable, so a cache > > flush is required before they can be DMA'd. Hence the streaming > > API. > > Is the syscall "cacheflush()" supposed to be the knob for that? > > Or is there any other ones to have more precise control, "clean", > "invalidate" and "flush", from userland in generic way? No other syscalls are required - this sequence will do everything you need to perform DMA on pages mapped into userspace: get_user_pages() convert array of struct page * to scatterlist dma_map_sg() perform DMA dma_unmap_sg() for each page in sg() page_cache_release(page); If you get the list of pages some other way (eg, via shmem_read_mapping_page_gfp) then additional maintanence may be required (though that may be a bug in shmem - remember this stuff hasn't been well tested on ARM before.) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/