Re: [RFC 4/4] drm: Add NVIDIA Tegra support

[Thierry Reding <thierry.reding-RM9K5IK7kjKj5M59NBduVrNAH6kLmebB@public.gmane.org>]

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* Marek Szyprowski wrote:
> Hi Thierry,
> 
> On Thursday, April 12, 2012 9:18 AM Thierry Reding wrote:
> > Also this doesn't yet solve the vmap() problem that is needed for the kernel
> > virtual mapping. I did try using dma_alloc_writecombine(), but that only
> > works for chunks of 2 MB or smaller, unless I use init_consistent_dma_size()
> > during board setup, which isn't provided for in a DT setup. I couldn't find
> > a better alternative, but I admit I'm not very familiar with all the VM APIs.
> > Do you have any suggestions on how to solve this? Otherwise I'll try and dig
> > in some more.
> 
> Yes, I'm aware of this issue I'm currently working on solving it. I hope to use 
> standard vmalloc range for all coherent/writecombine allocations and get rid of
> the custom 'consistent_dma' region at all.

Does your work aim at removing the 2 MB limitation or at remapping non-
contiguous memory to a virtually linear buffer? I have some trouble
understanding how removing the 2 MB limit would help, because if all buffers
can be allocated contiguously then there wouldn't be any need for the IOMMU,
right?

Thierry

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