Hello Marek I have prepared a new set of patches, please take a look to them. The series implements the coherent allocation, segments compaction and use of sg_table, it does not implement the dma_map/dma_unmap/dma_sync, I rather work on that one when you are back.
Thanks for your help On Thu, Jul 18, 2013 at 3:34 PM, Marek Szyprowski <m.szyprow...@samsung.com> wrote: > Hello, > > > On 7/18/2013 9:39 AM, Ricardo Ribalda Delgado wrote: >> >> Hello again: >> >> I have started to implemt it, but I think there is more hidden work in >> this task as it seems. In order to call dma_map_sg and >> max_dma_segment_size I need acess to the struct device, but (correct >> me if I am wrong), vb2 is device agnostic. Adding the above >> functionality will mean not only updating marvell-ccic and solo6x10, >> but updating all the vb2 buffers. > > > For getting device pointer, vb2-dma-sg need to be extended with so called > 'allocator context'. Please check how it is done in vb2-dma-contig > (vb2_dma_contig_init_ctx() function). > > > >> Also after some readings, maybe the sg compactation should not be done >> here, but in dma_map_sg. According to the doc: >> >> """ >> The implementation is free to merge several consecutive sglist entries >> into one (e.g. if DMA mapping is done with PAGE_SIZE granularity, any >> consecutive sglist entries can be merged into one provided the first one >> ends and the second one starts on a page boundary - in fact this is a huge >> advantage for cards which either cannot do scatter-gather or have very >> limited number of scatter-gather entries) and returns the actual number >> of sg entries it mapped them to. On failure 0 is returned. >> """ >> >> So, my proposal would be to alloc with alloc_pages to try to get >> memory as coherent as possible, then split the page, set the sg in >> PAGE_SIZE lenghts, and then let the dma_map_sg do its magic. if it >> doesnt do compactation, fix dma_map_sg, so more driver could take >> advantage of it. > > > Right, this approach is probably the best one, but this way you would need > to do the compaction in every dma-mapping implementation for every supported > architecture. IMHO vb2-dma-sg can help dma-mapping by at least by allocating > memory in larger chunks and constructing shorter scatter list. Updating > dma-mapping functions across all architectures is a lot of work and testing, > so for initial version we should focus on vb2-dma-sg. Memory allocators > already do some work to ease mapping a buffer to dma space. > > >> I could also of course fix marvell-ccic and solo6x10 to use sg_table. >> >> Does anything of this make sense? > > > I would also like to help you as much as possible, but for the next 10 days > I will be not available for both personal reasons and holidays. If you have > any questions, feel free to leave them on my mail, I will reply asap I get > back. > > > Best regards > -- > Marek Szyprowski > Samsung R&D Institute Poland > > -- Ricardo Ribalda -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
