Re: [PATCH v11 2/9] iommu/arm-smmu-v3: Enforce arm_smmu_cmdq_build_sync_cmd

[Will Deacon <will@kernel.org>]

On Tue, Aug 06, 2024 at 07:11:47PM -0700, Nicolin Chen wrote:
> There is an existing arm_smmu_cmdq_build_sync_cmd() so the driver should
> call it at all places other than going through arm_smmu_cmdq_build_cmd()
> separately. This helps the following patch that adds a CS_NONE option.
> 
> Note that this changes the type of CMD_SYNC in __arm_smmu_cmdq_skip_err,
> in ARM_SMMU_OPT_MSIPOLL=true case, from previously a non-MSI one to now
> an MSI one that is proven to still work using a hacking test:
>   nvme: Adding to iommu group 10
>   nvme: --------hacking-----------
>   arm-smmu-v3: unexpected global error reported (0x00000001),
>                this could be serious
>   arm-smmu-v3: CMDQ error (cons 0x01000022): Illegal command
>   arm-smmu-v3: skipping command in error state:
>   arm-smmu-v3:  0x0000000000000000
>   arm-smmu-v3:  0x0000000000000000
>   nvme: -------recovered----------
>   nvme nvme0: 72/0/0 default/read/poll queues
>    nvme0n1: p1 p2

Hmm, I'm still a little wary of this. The only reason we emit a CMD_SYNC
in __arm_smmu_cmdq_skip_err() is because the SMMU doesn't have a NOP
command. So I'd really like the SYNC to have as little functionality
as possible in this case.

I think we could either propapate the 'cs' field down to
arm_smmu_cmdq_build_cmd() or just open-code the command-creation in
__arm_smmu_cmdq_skip_err().

Will