Messages in this thread |  | | From | "Lee, Shuyu" <> | Subject | How to DMA data from a pci device to a user buffer directly | Date | Mon, 5 May 2003 15:49:23 -0400 |
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Hello, All.
In my device driver, I want to DMA image data from a PCI device (a frame grabber) to a user buffer directly. Right now I am stuck at how to convert a user virtual address to a physical address that can be used by the DMA controller.
Here is my sequence: 1) User allocates an image buffer, 2) User passes the pointer (pUserVirtualAddr) of that buffer to the driver through an ioctl call, 3) Driver calls alloc_kiovec(1, &iobuf); 4) Driver calls map_user_kiobuf(WRITE, iobuf, (ULONG)pUserVirtualAddr, imageBufferSize); I believe map_user_kiobuf() is executed successfully, for the following reasons: 1) map_user_kiobuf() returns 0, 2) For imageBufferSize = 640*160, iobuf->nr_pages = 26. Because pUserVirtualAddr is not page-aligned, 26 is correct. 3) iobuf->offset is equal to (ULONG)pUserVirtualAddr & 0xFFF, which is also correct. What is strange to me is that iobuf->maplist[idx]->virtual = 0 for idx = 0,1,2,...,25.
One driver developer suggested that I do the following to get the physical address for the first page: physAddr = virt_to_bus(page_address(iobuf->maplist[0])) + iobuf->offset; Because page_address() is "#define page_address(page) ((page)->virtual)" and "virtual" is equal to 0, this approach will not work for me.
Another suggested that I add this to my code: #define page_to_bus(page) \ (ULONG)(((page) - mem_map) << PAGE_SHIFT), and get the physical address for the first page this way: physAddr = page_to_bus(iobuf->maplist[0])+iobuf->offset; Because it is not clear to me what exactly is "mem_map", I am not sure how "maplist" of type "struct page*", is subtracted by "mem_map" of type "mem_map_t*". In my test, I have: 1) maplist[0] = 0xC114ECEC; 2) mem_map = 0xC1000010. Ignore the offset, what the physical address should be?
My development environment: 1) OS: RedHat 7.2 (2.4.7-10) 2) GCC: 3.2.1 3) PC: P-III single processor w/ 128Mbytes of memory, 4) BUS: PCI, 5) My DMA controller has unlimited scatter-gather capability.
By the way, I have tested the rest of my code by DMA the image data to a kernel buffer allocated using kmalloc() first, then do a memcpy() to copy the image data to a user buffer. This alternative seems to work fine.
All suggestions and comments are greatly appreciated. Shuyu
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