From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Date: Thu, 20 Aug 2020 16:52:13 +0000 Subject: Re: [PATCH 05/28] media/v4l2: remove V4L2-FLAG-MEMORY-NON-CONSISTENT Message-Id: <20200820165213.GC12693@lst.de> List-Id: References: <20200819065555.1802761-1-hch@lst.de> <20200819065555.1802761-6-hch@lst.de> <62e4f4fc-c8a5-3ee8-c576-fe7178cb4356@arm.com> <2b32f1d8-16f7-3352-40a5-420993d52fb5@arm.com> <20200820050214.GA4815@lst.de> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Tomasz Figa Cc: Christoph Hellwig , Robin Murphy , alsa-devel@alsa-project.org, linux-ia64@vger.kernel.org, Linux Doc Mailing List , nouveau@lists.freedesktop.org, linux-nvme@lists.infradead.org, Linux Kernel Mailing List , "James E.J. Bottomley" , linux-mm@kvack.org, Marek Szyprowski , linux-samsung-soc , Joonyoung Shim , linux-scsi@vger.kernel.org, Kyungmin Park , Ben Skeggs , Matt Porter , Linux Media Mailing List , Tom Lendacky , Pawel Osciak , Mauro Carvalho Chehab , "list@263.net:IOMMU DRIVERS" , Joerg Roedel , "list@263.net:IOMMU DRIVERS , Joerg Roedel ," , Thomas Bogendoerfer , linux-parisc@vger.kernel.org, netdev@vger.kernel.org, Seung-Woo Kim , linux-mips@vger.kernel.org On Thu, Aug 20, 2020 at 12:24:31PM +0200, Tomasz Figa wrote: > > Of course this still uses the scatterlist structure with its annoying > > mix of input and output parametes, so I'd rather not expose it as > > an official API at the DMA layer. > > The problem with the above open coded approach is that it requires > explicit handling of the non-IOMMU and IOMMU cases and this is exactly > what we don't want to have in vb2 and what was actually the job of the > DMA API to hide. Is the plan to actually move the IOMMU handling out > of the DMA API? > > Do you think we could instead turn it into a dma_alloc_noncoherent() > helper, which has similar semantics as dma_alloc_attrs() and handles > the various corner cases (e.g. invalidate_kernel_vmap_range and > flush_kernel_vmap_range) to achieve the desired functionality without > delegating the "hell", as you called it, to the users? Yes, I guess I could do something in that direction. At least for dma-iommu, which thanks to Robin should be all you'll need in the foreseeable future.