[PATCH v4 18/23] iommu/arm-smmu-v3-iommufd: Support implementation-defined hw_info

[Nicolin Chen]

On Thu, May 15, 2025 at 03:56:29PM -0300, Jason Gunthorpe wrote:
> On Thu, May 15, 2025 at 11:52:05AM -0700, Nicolin Chen wrote:
> > On Thu, May 15, 2025 at 02:17:06PM -0300, Jason Gunthorpe wrote:
> > > On Thu, May 08, 2025 at 08:02:39PM -0700, Nicolin Chen wrote:
> > Should the first call return out_data_type=CMDQV while returning
> > the arm_smmu_v3 hw_info data? Otherwise, VMM wouldn't know what
> > to set in the input sub_data_type of the 2nd ioctl?
> 
> No, either set a flag in the smmu_v3 hw_info, as you were doing here,
> or just have the vmm probe it. Given the VMM is likely to be told to
> run in vCMDQ mode on the command line try-and-fail doesn't sound so
> bad.
> 
> And I guess we don't need a "sub type" just a "requested type" where 0
> means return the best one and non-zero means return a specific one or
> fail with EOPNOTSUPP.

OK. I think this would work:
hw_info (req_type=0)     => out_data_type=SMMU_V3, flags=HAS_CMDQV
hw_info (req_type=CMDQV) => out_data_type=CMDQV,   flags=0

Or, would it be simpler by having a sub_data_uptr:
hw_info => out_data_type=SMMU_V3, sub_data_type=CMDQV,
           data_uptr=iommu_hw_info_arm_smmuv3,
	   sub_data_uptr=iommu_hw_info_tegra241_cmdqv
?

Thanks
Nicolin