On Fri, Jun 14, 2019 at 04:02:39PM +0200, Greg KH wrote:

Perhaps a hint as to how we can fix this up?  This is the first time
I've heard of the comedi code not handling dma properly.

It can be fixed by:

 a) never calling virt_to_page (or vmalloc_to_page for that matter)
    on dma allocation
 b) never remapping dma allocation with conflicting cache modes
    (no remapping should be doable after a) anyway).

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