DMA from high memory regions

[Imran Badr]

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.