On 04/20/2015 12:37 AM, Alexandre Courbot wrote:
I don't have a strong opinion on this - the advantage of a bit mask
over a bit index is that it at least gives us the option of not having
a MMU translation bit at all (mask == 0) whereas a bit index of 0 will
set/unset the first bit.
Not that we need this for now, but keeping that possibility open
doesn't sound bad for the future (nothing guarantees the GPU will
always be behind the IOMMU).
We should not rely only on globally enabling / disabling IOMMU. The mask
you describe is global. We'll want to bypass IOMMU, but we'll want to
do that in the mapping code path per buffer. VPR is an example: VPR
buffers would sometimes be touched by GPU, and GPU needs to bypass
IOMMU. But interleaved with that GPU is also using normal buffers with
IOMMU translation.
Of course, sometimes we want to bypass IOMMU globally. So it's good to
have also a mechanism to disable IOMMU for the whole GPU.
Terje
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