RE: DMA from high memory regions

From: Imran Badr (imran.badr@cavium.com)
Date: Wed Jun 26 2002 - 11:43:22 EST

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Many thanks for the reply. It sure works and I noticed that code in
pci_map_page() api. Previously I was using kernel 2.4.2 fron RedHat7.1 which
has no such kernel function.
Now, if I need to access that page in my device driver, how can I get kernel
virtual address without using kmap?

Thanks,
Imran.

-----Original Message-----
From: Larry Sendlosky [mailto:Larry.Sendlosky@storigen.com]
Sent: Wednesday, June 26, 2002 6:33 AM
To: imran.badr@cavium.com
Subject: RE: DMA from high memory regions

There is no need to kmap.

1) call map_user_kiobuf to make sure buffer is mapped and pages
are not swapped.

2) call lock_kiovec to lock the pages for I/O

3) use the struct page pointers in the kiobuf maplist
   to compute physical page address of each page.
   eg ((struct_page_pointer - mem_map) << PAGE_SHIFT) is physical
   address of the page described by 'struct page *struct_page_pointer'.

You now have the physical addresses needed to give to the device
for DMA.

-----Original Message-----
From: Imran Badr [mailto:imran.badr@cavium.com]
Sent: Tuesday, June 25, 2002 7:30 PM
To: 'lkml'
Subject: DMA from high memory regions

Hi,

I am trying to setup DMA to/from user space. I get a user pointer in my
device driver, from which I build up kiobuf and call map_user_kiobuf. After
this, I call kmap to map pages to kernel virtual space and then virt_to_bus
to get bus address. Now if I define CONFIG_HIGHMEM and that page happens to
be in the memory region near 1GB then DMA never happens and I donot see any
data in result pointer. If CONFIG_HIGHMEM is not defined, then everything
works perfectly. Please suggest any solution.

Thanks,
Imran.

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