Re: [RFC 7/7] iommu/core: split mapping to page sizes as supported bythe hardware

[KyongHo Cho]

Hi

On Sat, Sep 3, 2011 at 2:32 AM, Ohad Ben-Cohen <ohad@xxxxxxxxxx> wrote:
> When mapping a memory region, split it to page sizes as supported
> by the iommu hardware. Always prefer bigger pages, when possible,
> in order to reduce the TLB pressure.
>
True. It is important for the peripheral devices that works with IOMMU.

> This allows a more lenient granularity of mappings: traditionally the
> IOMMU API took 'order' (of a page) as a mapping size, and directly let
> the low level iommu drivers handle the mapping. Now that the IOMMU
> core can split arbitrary memory regions into pages, we can remove this
> limitation, so users don't have to split those regions by themselves.
>

Please find the following link that I submitted for our IOMMU.
https://lkml.org/lkml/2011/7/3/152

s5p_iommu_map/unmap accepts any order of physical address and iova
without support of your suggestion if the order is not less than PAGE_SHIFT

Of course, an IO virtual memory manager must be careful when it allocates
IO virtual memory to lead best performance.
But I think IOMMU API must not expect that the caller of iommu_map() knows
about the restriction of IOMMU API implementation.

Regards,
Cho KyongHo.
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