Re: mmap

[Gerd Knorr <kraxel@bytesex.org>]

mdaljeet@in.ibm.com wrote:
>  I am doing the following:
>  
>     malloc some memory is user space
>     pass its pointer to some kernel module
>     in the kernel module...do a pci_alloc_consistent so that i get a memory
>     region for PCI DMA operations

Wrong approach, you can use kiobufs if you want DMA to the malloc()ed
userspace memory:

 * lock down the user memory using map_user_kiobuf() + lock_kiovec()
   (see linux/iobuf.h).
 * translate the iobuf->maplist into a scatterlist [1]
 * feed pci_map_sg() with the scatterlist to get DMA addresses.
   you can pass to the hardware.

And the reverse to free everything when you are done of course.

  Gerd

[1] IMHO it would be more useful if iobufs would use a scatterlist
    instead of an struct page* array.


-- 
Gerd Knorr <kraxel@bytesex.org>  --  SuSE Labs, Außenstelle Berlin