From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: [PATCH 3/3] videobuf2: replace a layering violation with dma_map_resource Date: Thu, 17 Jan 2019 18:21:52 +0100 Message-ID: <20190117172152.GA32292@lst.de> References: <20190111181731.11782-1-hch@lst.de> <20190111181731.11782-4-hch@lst.de> <6f8892ac-c2aa-10df-c74f-ba032bf75160@samsung.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <6f8892ac-c2aa-10df-c74f-ba032bf75160@samsung.com> Sender: linux-kernel-owner@vger.kernel.org To: Marek Szyprowski Cc: Christoph Hellwig , Pawel Osciak , Kyungmin Park , Niklas =?iso-8859-1?Q?S=F6derlund?= , Russell King , Mauro Carvalho Chehab , iommu@lists.linux-foundation.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, linux-media@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: iommu@lists.linux-foundation.org On Mon, Jan 14, 2019 at 01:42:26PM +0100, Marek Szyprowski wrote: > Hi Christoph, > > On 2019-01-11 19:17, Christoph Hellwig wrote: > > vb2_dc_get_userptr pokes into arm direct mapping details to get the > > resemblance of a dma address for a a physical address that does is > > not backed by a page struct. Not only is this not portable to other > > architectures with dma direct mapping offsets, but also not to uses > > of IOMMUs of any kind. Switch to the proper dma_map_resource / > > dma_unmap_resource interface instead. > > > > Signed-off-by: Christoph Hellwig > > There are checks for IOMMU presence in other places in vb2-dma-contig, > so it was used only when no IOMMU is available, but I agree that the > hacky code should be replaced by a generic code if possible. > > Tested-by: Marek Szyprowski > > V4L2 pipeline works fine on older Exynos-based boards with CMA and IOMMU > disabled. Do you know if these rely on the offsets? E.g. would they still work with the patch below applied on top. That would keep the map_resource semantics as-is as solve the issue pointed out by Robin for now. If not I can only think of a flag to bypass the offseting for now, but that would be pretty ugly. Or go for the long-term solution of discovering the relationship between the two devices, as done by the PCIe P2P code.. diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c index 8e0359b04957..25bd19974223 100644 --- a/kernel/dma/direct.c +++ b/kernel/dma/direct.c @@ -359,7 +359,7 @@ EXPORT_SYMBOL(dma_direct_map_sg); dma_addr_t dma_direct_map_resource(struct device *dev, phys_addr_t paddr, size_t size, enum dma_data_direction dir, unsigned long attrs) { - dma_addr_t dma_addr = phys_to_dma(dev, paddr); + dma_addr_t dma_addr = paddr; if (unlikely(!dma_direct_possible(dev, dma_addr, size))) { report_addr(dev, dma_addr, size);