Re: IOVA allocation dependency between firmware buffer and remaining buffers

[Ajay Kumar <ajaykumar.rs1989@gmail.com>]

Hello all,

We pretty much tried to solve the same issue here with a new API in DMA-IOMMU:
https://lore.kernel.org/linux-iommu/20200811054912.GA301@infradead.org/T/

Christoph - the user part would be MFC devices on exynos platforms

Thanks,
Ajay


On Wed, Sep 23, 2020 at 12:28 PM Christoph Hellwig <hch@lst.de> wrote:
>
> On Wed, Sep 23, 2020 at 08:48:26AM +0200, Marek Szyprowski wrote:
> > Hi Shaik,
> >
> > I've run into similar problem while adapting S5P-MFC and Exynos4-IS
> > drivers for generic IOMMU-DMA framework. Here is my first solution:
> > https://lore.kernel.org/linux-samsung-soc/20200918144833.14618-1-m.szyprowski@samsung.com/T/
> >
> >
> > 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.
>
> If you want to use IOVA addresses in a device otherwise managed by
> dma-iommu we need to expose an API through the dma API.  Can you please
> include the iommu list in the discussion of your series?
>
> I don't think using the raw IOMMU API is a very idea in these drivers,
> we probably want a way to change the allocator algorithm or hint the
> next IOVA and keep using the normal DMA API.  Maybe Robin has a better
> idea.
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