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. 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. 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>