Hi Russell, 2012/10/16 Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx>: > On Tue, Oct 16, 2012 at 07:12:49PM +0900, Inki Dae wrote: >> Hi Hiroshi, >> >> I'm not sure I understand what you mean but we had already tried this >> way and for this, you can refer to below link, >> http://www.mail-archive.com/dri-devel@xxxxxxxxxxxxxxxxxxxxx/msg22555.html >> >> but this way had been pointed out by drm guys because the pages could >> be used through gem object after that pages had been freed by free() >> anyway their pointing was reasonable and I'm trying another way, this >> is the way that the pages to user space has same life time with dma >> operation. in other word, if dma completed access to that pages then >> also that pages will be freed. actually drm-based via driver of >> mainline kernel is using same way > > I don't know about Hiroshi, but the above "sentence" - and I mean the 7 > line sentence - is very difficult to understand and wears readers out. > Sorry for this. Please see below comments. > If your GPU hardware has a MMU, then the problem of dealing with userspace > pages is very easy. Do it the same way that the i915 driver and the rest > of DRM does. Use shmem backed memory. > > I'm doing that for the Dove DRM driver and it works a real treat, and as > the pages are backed by page cache pages, you can use all the normal > page refcounting on them to prevent them being freed until your DMA has > completed. All my X pixmaps are shmem backed drm objects, except for > the scanout buffers which are dumb drm objects (because they must be > contiguous.) > > In fact, get_user_pages() will take the reference for you before you pass > them over to dma_map_sg(). On completion of DMA, you just need to use > dma_unmap_sg() and release each page. > It's exactly same as ours. Besides, I know get_user_pages() takes 2 reference counts if the user process has never accessed user region allocated by malloc(). Then, if the user calls free(), the page reference count becomes 1 and becomes 0 with put_page() call. And the reverse holds as well. This means how the pages backed are used by dma and freed. dma_map_sg() just does cache operation properly and maps these pages with iommu table. There may be my missing point. Thanks, Inki Dae > If you don't want to use get_user_pages() (which other drivers don't) then > you need to following the i915 example and get each page out of shmem > individually. > > (My situation on the Dove hardware is a little different, because the > kernel DRM driver isn't involved with the GPU - it merely provides the > memory for pixmaps. The GPU software stack, being a chunk of closed > source userspace library with open source kernel driver, means that > things are more complicated; the kernel side GPU driver uses > get_user_pages() to pin them prior to building the GPU's MMU table.) > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@xxxxxxxxx. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>