Hi Tim, On Wed, Mar 18, 2015 at 03:58:07PM -0500, Tim Nordell wrote: > Laurent - > > On 03/18/15 14:49, Tim Nordell wrote: > >Digging through to find who is responsible for assigning the virtual > >addresses, I find that it's buried inside > >arch/arm/mm/dma-mapping.c:__alloc_iova(...). This call is called > >individually for each entry in the scatter-gather table via > >__map_sg_chunk from iommu_map_sg(...). If this is supposed to allocate > >a contiguous virtual memory region, it seems that __iommu_map_sg(...) > >should be considering the full buffer range rather than parts of the > >buffer at a time for the virtual allocation, similar to how > >__iommu_create_mapping(...) works in the same file. > > > >- Tim > > > > I've confirmed that this code is the culprit for allocating a > non-contiguous space (called via the dma_map_sg_attrs(...) back down > in the videobuf2-dma-contig). I've reworked it for testing so that > it does an __alloc_iova(...) on the entire region rather than a > chunk at a time, however, I don't think what I have locally is > completely the right approach for the generic case since I think > technically a given entry in the scatterlist could end up with the > end of a page partially used (the per list entry ->offset and such). > > Looks like code (the specific functions in mm/dma-mapping.c) in > question was last touched in 2012 with a quick git-blame, but I > don't know how long the OMAP 3 ISP code has been using this common > code. I'm guessing it's only been since the virtual memory manager > internal to the IOMMU code was removed in July of last year. I don't think omap3isp has been using this very long. A few minor versions perhaps. > Do you know if this common code is supposed to guarantee a > physically contiguous memory region? The documentation for the > function doesn't indicate that it should, and it certainly doesn't > as-is. It seems like hitting this issue is highly dependent on the > size of the buffer one is allocating. I guess there aren't too many drivers that may map large areas of memory pinned using get_user_pages() to IOMMU. If dma_map_sg() couldn't be used to allocate virtually contiguous memory, then what could be? This looks like a bug in __iommu_map_sg() to me. Cc the iommu list. -- Kind regards, Sakari Ailus e-mail: sakari.ailus@xxxxxx XMPP: sailus@xxxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
