RE: [PATCH v7 7/9] iommu/vt-d: Allow qi_submit_sync() to return the QI faults

[Tian, Kevin]

> From: Liu, Yi L <yi.l.liu@xxxxxxxxx>
> Sent: Tuesday, December 26, 2023 4:44 PM
> 
> On 2023/12/26 14:15, Yi Liu wrote:
> >
> >
> > On 2023/12/26 12:13, Tian, Kevin wrote:
> >>> From: Liu, Yi L <yi.l.liu@xxxxxxxxx>
> >>> Sent: Tuesday, December 26, 2023 12:03 PM
> >>>
> >>> On 2023/12/22 12:23, Tian, Kevin wrote:
> >>>>> From: Liu, Yi L <yi.l.liu@xxxxxxxxx>
> >>>>> Sent: Thursday, December 21, 2023 11:40 PM
> >>>>>
> >>>>> +    fault &= DMA_FSTS_IQE | DMA_FSTS_ITE | DMA_FSTS_ICE;
> >>>>> +    if (fault) {
> >>>>> +        if (fsts)
> >>>>> +            *fsts |= fault;
> >>>>
> >>>> do we expect the fault to be accumulated? otherwise it's clearer to
> >>>> just do direct assignment instead of asking for the caller to clear
> >>>> the variable before invocation.
> >>>
> >>> not quite get. do you mean the fault should not be cleared in the caller
> >>> side?
> >>>
> >>
> >> I meant:
> >>
> >>     if (fsts)
> >>         *fsts = fault;
> >>
> >> unless there is a reason to *OR* the original value.
> >
> > I guess no such a reason. :) let me modify it.
> 
> hmmm, replied too soon. The qi_check_fault() would be called multiple
> times in one invalidation circle as qi_submit_sync() needs to see if any
> fault happened before the hw writes back QI_DONE to the wait descriptor.
> There can be ICE which may eventually result in ITE. So caller of
> qi_check_fault()
> would continue to wait for QI_DONE. So qi_check_fault() returns 0 to let
> qi_submit_sync() go on though ICE detected. If we use '*fsts = fault;',
> then ICE would be missed since the input fsts pointer is the same in
> one qi_submit_sync() call.
> 

ok, that makes sense then.