On Jul 16 2004, at 15:11, Amit D. Chaudhary was caught saying:Thanks, noted and verified.
I am missing what you are directing me to.
If it is,
They internally seem to __get_free_pages()
Correct, but take a second look at the code (2.6):
/* ignore region specifiers */
gfp &= ~(__GFP_DMA | __GFP_HIGHMEM);
if (dev == NULL || (dev->coherent_dma_mask < 0xffffffff))
gfp |= GFP_DMA;
ret = (void *)__get_free_pages(gfp, get_order(size));
It uses GFP_DMA iff your coherent_dma_mask is != 0xffffffff. Assuming
your device can address a the full 32-bit PCI address space, you
need to set the coherent_dma_mask appropriately and you will get
buffers from all addressable lowmem. I don't do much x86, so not
sure how you go about allocating highmem DMA buffers.
This was a backup approach, I mentioned to provide details about the memory being allocated. I would like to avoid this approach. See reasons above.The memory need not be page size, as a matter of fact, using a large consecutive block, for example using alloc_bootmem_low() during kernel bootup, will simplify the data transfer and result in no internal fragmentation, it does introduce inflexibility in changing the size and other issues.
If you are using alloc_bootmem_low(), all you should have to do after
allocating the memory is call pci_dma_map_single()/map_sg() to get PCI-DMA addresses. You still should have no reason to touch MAX_DMA_ADDRESS.