Re: [PATCH 16/18] staging/media/tegra-vde: Clean up IOMMU workaround

27.08.2020 18:54, Thierry Reding пишет:
...

quoted

The Tegra DRM has a very special quirk for ARM32 that was added in this
commit [2] and driver relies on checking of whether explicit or implicit
IOMMU is used in order to activate the quirk.

[2]
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=273da5a046965ccf0ec79eb63f2d5173467e20fa

Once the implicit IOMMU is used for the DRM driver, the quirk no longer
works (if I'm not missing something). This problem needs to be resolved
before implicit IOMMU could be used by the Tegra DRM on ARM32.

...

I do have a patch lying around somewhere that implements the mapping
cache that was referenced in the above commit. Let me know if I should
dig that up and send it out.

Hello, Thierry! It certainly will be interesting to take a look at yours
patch!

I think that the caching shouldn't be strictly necessary for keeping the
current workaround working and it should be possible to keep the code
as-is by replacing the domain-type checking with the SoC-generation
check in the Tegra DRM driver.

In general, IMO it should be better to stash the complex changes until
we'll get closer to adopting the new UAPI as it will certainly touch the
aspect of the per-device mappings. But if yours patch is less than 100
LOC, then maybe we could consider applying it right now!

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