Hi Joerg,

On 24.09.2020 10:28, Joerg Roedel wrote:
> On Wed, Sep 23, 2020 at 08:48:26AM +0200, Marek Szyprowski wrote:
>> It allows to remap given buffer at the specific IOVA address, although
>> it doesn't guarantee that those specific addresses won't be later used
>> by the IOVA allocator. Probably it would make sense to add an API for
>> generic IOMMU-DMA framework to mark the given IOVA range as
>> reserved/unused to protect them.
> There is an API for that, the IOMMU driver can return IOVA reserved
> regions per device and the IOMMU core code will take care of mapping
> these regions and reserving them in the IOVA allocator, so that
> DMA-IOMMU code will not use it for allocations.
>
> Have a look at the iommu_ops->get_resv_regions() and
> iommu_ops->put_resv_regions().

I know about the reserved regions IOMMU API, but the main problem here, 
in case of Exynos, is that those reserved regions won't be created by 
the IOMMU driver but by the IOMMU client device. It is just a result how 
the media drivers manages their IOVA space. They simply have to load 
firmware at the IOVA address lower than the any address of the used 
buffers.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland

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