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

Jason Gunthorpe
2025-05-15T19:23:33Z

On Thu, May 15, 2025 at 12:21:17PM -0700, Nicolin Chen wrote:
> 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

Yeah

> 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
> ?

I think the former is simpler to code, you can just add the req_type
to the signatures and if the driver comes back with a type != req_type
the core code will return EOPNOTSUPP

Then just match the impl_ops for req_type in the arm driver.

Finally we end up with only one ioctl enum number space for the
types, which seems appealing.

Jason