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Date: Mon, 17 Nov 2014 14:43:46 +0000 From: David Vrabel <david.vrabel@...rix.com> To: Stefano Stabellini <stefano.stabellini@...citrix.com>, <gregkh@...uxfoundation.org> CC: <linux-mips@...ux-mips.org>, <airlied@...ux.ie>, <dri-devel@...ts.freedesktop.org>, <xen-devel@...ts.xensource.com>, <linux@....linux.org.uk>, <vinod.koul@...el.com>, <deller@....de>, <jejb@...isc-linux.org>, Ian Campbell <Ian.Campbell@...rix.com>, <alexander.deucher@....com>, <bhelgaas@...gle.com>, <linux-arm-kernel@...ts.infradead.org>, <linux-parisc@...r.kernel.org>, <dwmw2@...radead.org>, <linux-kernel@...r.kernel.org>, <ralf@...ux-mips.org>, <iommu@...ts.linux-foundation.org>, David Vrabel <david.vrabel@...rix.com>, <dmaengine@...r.kernel.org>, <torvalds@...ux-foundation.org>, <christian.koenig@....com> Subject: Re: [Xen-devel] [RFC] add a struct page* parameter to dma_map_ops.unmap_page On 17/11/14 14:11, Stefano Stabellini wrote: > Hi all, > I am writing this email to ask for your advice. > > On architectures where dma addresses are different from physical > addresses, it can be difficult to retrieve the physical address of a > page from its dma address. > > Specifically this is the case for Xen on arm and arm64 but I think that > other architectures might have the same issue. > > Knowing the physical address is necessary to be able to issue any > required cache maintenance operations when unmap_page, > sync_single_for_cpu and sync_single_for_device are called. > > Adding a struct page* parameter to unmap_page, sync_single_for_cpu and > sync_single_for_device would make Linux dma handling on Xen on arm and > arm64 much easier and quicker. Using an opaque handle instead of struct page * would be more beneficial for the Intel IOMMU driver. e.g., typedef dma_addr_t dma_handle_t; dma_handle_t dma_map_single(struct device *dev, void *va, size_t size, enum dma_data_direction dir); void dma_unmap_single(struct device *dev, dma_handle_t handle, size_t size, enum dma_data_direction dir); etc. Drivers would then use: dma_addr_t dma_addr(dma_handle_t handle); To obtain the bus address from the handle. > I think that other drivers have similar problems, such as the Intel > IOMMU driver having to call find_iova and walking down an rbtree to get > the physical address in its implementation of unmap_page. > > Callers have the struct page* in their hands already from the previous > map_page call so it shouldn't be an issue for them. A problem does > exist however: there are about 280 callers of dma_unmap_page and > pci_unmap_page. We have even more callers of the dma_sync_single_for_* > functions. You will also need to fix dma_unmap_single() and pci_unmap_single() (another 1000+ callers). You may need to consider a parallel set of map/unmap API calls that return/accept a handle, and then converting drivers one-by-one as required, instead of trying to convert every single driver at once. David -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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