Kumar Gala wrote:
On Dec 12, 2008, at 3:04 AM, Trent Piepho wrote:
On Thu, 11 Dec 2008, Kumar Gala wrote:
On Dec 11, 2008, at 10:07 PM, Trent Piepho wrote:
Don't the ATMU windows in the pcie controller serve as a IOMMU, making
swiotlb
unnecessary and wasteful?
Nope. You have no way to tell when to switch a window as you have no
idea
when a device might DMA data.
Isn't that what dma_alloc_coherent() and dma_map_single() are for?
Nope. How would manipulate the PCI ATMU?
It could dynamically set up 1GB or so windows to cover
currently-established mappings as they happen, and fall back on bounce
buffering if no windows are available. This avoids penalizing a
DMA-heavy application that is the only DMA user (so no window
thrashing), but happens to live in high memory.
That said, let's get things working first, and optimize later.
-Scott
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