Re: mmap

[mdaljeet@in.ibm.com]

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I use the 'map_user_kiobuf' and 'lock_kiovec' kernel routines in a module
for 'user space memory'. After that if I pass the
'(iobuf->maplist[0])-mem_map) <<  PAGE_SHIFT)' to the hardware for DMA
operations and it works fine for Intel platforms. Now how can I use the
'iobuf' struct obtained after lock_kiovec operation to get a PCI bus
address that I can pass to hardware for DMA operations on my Apple
machine.?

thanks,
Daljeet.


|--------+----------------------->
|        |          Gerd Knorr   |
|        |          <kraxel@bytes|
|        |          ex.org>      |
|        |                       |
|        |          05/15/01     |
|        |          01:03 PM     |
|        |          Please       |
|        |          respond to   |
|        |          Gerd Knorr   |
|        |                       |
|--------+----------------------->
  >-----------------------------------------------------------------------|
  |                                                                       |
  |       To:     linux-kernel@vger.kernel.org                            |
  |       cc:     (bcc: Daljeet Maini/India/IBM)                          |
  |       Subject:     Re: mmap                                           |
  >-----------------------------------------------------------------------|





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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
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