Leon Woestenberg wrote: > Hello Rolf Eike, > > On Fri, May 14, 2010 at 10:34 AM, Rolf Eike Beer <eike-kernel@xxxxxxxxx> wrote: > > Leon Woestenberg wrote: > >> Hello, > >> > >> my PCIe device supports 64-bit DMA for data, but only 32-bit addresses > >> for fetching descriptors from host memory. > >> > >> How can I allocate consistent memory in the 32-bit address range, even > >> though I earlier performed pci_set_dma_mask(..., DMA_64BIT_MASK)? > > > > Create a pci_pool (see pci_pool_*() in include/linux/pci.h) for the > > descriptors. Create the pool with a restriction to 32 bit. > > Thanks. Creating a pool with a restriction seems impossible: > > struct pci_pool *pci_pool_create(const char *name, struct pci_device *dev, > size_t size, size_t align, size_t alloc); > > However, subsequent allocation does allow restrictions: > > void *pci_pool_alloc(struct pci_pool *pool, gfp_t gfp_flags, > dma_addr_t *dma_handle); > > I had missed that in reading DMA-API.txt > > > What is the actual restriction flag for limiting to 32-bit? > > I can image this is hard to achieve, say, in a 36-bit physical system > (Intel PAE, PowerPC e500, ...) Ah, I confused that, sorry. The trick is like this: pci_set_dma_mask(pdev, DMA_BIT_MASK(32)) pci_set_consistent_dma_mask(pdev, DMA_BIT_MASK(64)) Eike
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