RE: [PATCH v6 2/6] iommufd: Add IOMMU_HWPT_INVALIDATE

[Tian, Kevin]

> From: Liu, Yi L <yi.l.liu@xxxxxxxxx>
> Sent: Monday, November 20, 2023 4:30 PM
> 
> On 2023/11/20 16:09, Tian, Kevin wrote:
> >> From: Liu, Yi L <yi.l.liu@xxxxxxxxx>
> >> Sent: Friday, November 17, 2023 9:07 PM
> >> + * @req_len: Length (in bytes) of a request entry in the request array
> >> + * @req_num: Input the number of cache invalidation requests in the
> array.
> >> + *           Output the number of requests successfully handled by kernel.
> >> + * @out_driver_error_code: Report a driver speicifc error code upon
> failure.
> >> + *                         It's optional, driver has a choice to fill it or
> >> + *                         not.
> >
> > Being optional how does the user tell whether the code is filled or not?
> 
> seems like we need a flag for it. otherwise, a reserved special value is
> required. or is it enough to just document it that this field is available
> or not per the iommu_hw_info_type?
> 

No guarantee that a reserved special value applies to all vendors.

I'll just remove the optional part. the viommu driver knows what a valid
code is, if the driver fills it.