Re: [PATCH v7 27/28] iommu/tegra241-cmdqv: Add user-space use support

Nicolin Chen
2025-07-02T00:50:35Z

On Wed, Jul 02, 2025 at 12:14:28AM +0000, Pranjal Shrivastava wrote:
> Thus, coming back to the two initial points:
>
> 1) Issuing "non-invalidation" commands through .cache_invalidate could
> be confusing, I'm not asking to change the op name here, but if we
> plan to label it, let's label them as "Trapped commands" OR
> "non-accelerated" commands as you suggested.

VCMDQ only accelerates limited invalidation commands, not all of
them: STE cache invalidation and CD cache invalidation commands
still go down to that op.

> 2) The "FIXME" confusion: The comment in arm_vsmmu_cache_invalidate
> mentions we'd like to "fix" the issuing of commands through the main
> cmdq and instead like to group by "type", if that "type" is the queue
> type (which I assume it is because IOMMU_TYPE has to be arm-smmu-v3),

I recall that FIXME is noted by Jason at that time. And it should
be interpreted as "group by opcode", IIUIC.

The thing is that for a host kernel that enabled in-kernel VCMDQs,
those trapped user commands can be just issued to the smmu->cmdq
or a vcmdq (picked via the get_secondary_cmdq impl_op).

> what do we plan to do differently there, given that the op is only
> for trapped commands *have* to go through the main CMDQ?

If we do something differently there, it could just do a one-time
get_secondary_cmdq call to pick a in-kernel vcmdq over smmu->cmdq
to fill in all the trapped commands.

And this is not related to this series at all.

Nicolin