On Wed, 18 Dec 2024 21:14:21 -0800, Nicolin Chen wrote:

The hardware limitation "max=19" actually comes from SMMU Command Queue.
So, it'd be more natural for tegra241-cmdqv driver to read it out rather
than hardcoding it itself.

This is not an issue yet for a kernel on a baremetal system, but a guest
kernel setting the queue base/size in form of IPA/gPA might result in a
noncontiguous queue in the physical address space, if underlying physical
pages backing up the guest RAM aren't contiguous entirely: e.g. 2MB-page
backed guest RAM cannot guarantee a contiguous queue if it is 8MB (capped
to VCMDQ_LOG2SIZE_MAX=19). This might lead to command errors when HW does
linear-read from a noncontiguous queue memory.

[...]

Applied to will (for-joerg/arm-smmu/updates), thanks!

[1/1] iommu/tegra241-cmdqv: Read SMMU IDR1.CMDQS instead of hardcoding
      https://git.kernel.org/will/c/e94dc6ddda8d

Cheers,
-- 
Will

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