Hi Group,
I have a few fundamental DMA questions which i need help with. These are all relating to kernel 2.6+.
I have 40 megs of memory set aside for DMA. (This is an embedded device so i can afford to do this). This memory is set aaside using the mem= option on the boot line. I need to DMA data to parts of this memory. The DMA card is a PCI based card with no addressing limitations. I want to make use of the
2.6 DMA API.
The reserved memory is given to anyone who requests it via the MMAP call, internally it uses remap_pfn_range to fix up the page tables.
Call sequence.
1. Userspace mmaps a large chuck on this memory, and then breaks it up into a chunk, and wants to DMA data from the imaging device to this chunck.
2. It fires an IOCTL to my driver passing a start pointer to this chunk and the len.
In the driver, i want to be able to
1. Create a scatter gather list for this chunk.
2. use pci_map_sg to map these pages.
3. use sg_address and sg_len to get the bus addresses.
4. using the bus address i want to populate the datastructures for this card and start the DMA.
Questions.
1. To generate the scatter gather list, i need to get a list of pages for the memory region passed to me? How do i do that? i know get_user_pages cannot be called since it does not work on VM_IO regions and remap_pfn_range marks the vma as VM_IO.
2. Is there any sample driver you know of which does similar stuff?
I'm open to suggestions and ideas.
rcn
