From: "Dave Airlie" <[EMAIL PROTECTED]> Date: Mon, 2 Apr 2007 09:44:41 +1000
> Okay I've got a bug reported before and now again about > 4GB + radeon > blows up the DRM... on Intel hw... > > What the drm currently does for the PCI GART table is it allocates a > chunk of memory (8MB) with vmalloc_32(), then when it decides to use > it it goes through every page of it calls pci_map_single() (with > PCI_DMA_TODEVICE, which is probably wrong...) with every page from the > vmalloc mapping and puts the bus addresses of the pages into the PCI > GART table on the GPU. > > So when swiotlb happens, as you can guess it all falls apart as the > drm never calls sync functions at any stage... You would have hit this on any platform that does caching in the PCI controller as well. > The main problem is the ring buffer and scratch write back, these > values are read/write from both the CPU and GPU quite a lot, so this > leads me to think I should really just be using dma_alloc_coherent for > the whole lot, however this is an 8MB mapping and possibly could be > getting larger in the future and dynamic as we do dynamic PCIEGART > support for the radeons... > > So I suppose I'm asking for ideas on the "correct" way to do this, and > perhaps any quick way to patch up the problem I'm seeing now by making > swiotlb not get involved .... Coherent memory was created for precisely the case where the cpu and the device frequently access the memory. 8MB is indeed a lot for the kind of allocation that the coherent DMA implementation uses. Does it really have to be all in one big 8MB chunk? I doubt it. Perhaps you can therefore create multiple DMA pools instead? See include/linux/dmapool.h ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys-and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV -- _______________________________________________ Dri-devel mailing list Dri-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/dri-devel
