Re: [PATCH] xen/arm: smmuv1: Revert associating the group pointer with the S2CR

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Mon, 19 Apr 2021, Rahul Singh wrote:
> Hi Julien,
> 
> > On 18 Apr 2021, at 6:48 pm, Julien Grall <julien@xxxxxxx> wrote:
> > 
> > 
> > 
> > On 16/04/2021 17:41, Rahul Singh wrote:
> >> Hi Julien
> > 
> > Hi Rahul,
> > 
> >>> On 16 Apr 2021, at 5:08 pm, Julien Grall <julien@xxxxxxx> wrote:
> >>> 
> >>> 
> >>> 
> >>> On 16/04/2021 17:05, Rahul Singh wrote:
> >>>>> On 16 Apr 2021, at 4:23 pm, Julien Grall <julien@xxxxxxx> wrote:
> >>>>> 
> >>>>> 
> >>>>> 
> >>>>> On 16/04/2021 16:01, Rahul Singh wrote:
> >>>>>> Hi Julien,
> >>>>> 
> >>>>> Hi Rahul,
> >>>>> 
> >>>>>>> On 16 Apr 2021, at 3:35 pm, Julien Grall <julien@xxxxxxx> wrote:
> >>>>>>> 
> >>>>>>> Hi,
> >>>>>>> 
> >>>>>>> On 16/04/2021 12:25, Rahul Singh wrote:
> >>>>>>>> Revert the code that associates the group pointer with the S2CR as 
> >>>>>>>> this
> >>>>>>>> code causing an issue when the SMMU device has more than one master
> >>>>>>>> device.
> >>>>>>> 
> >>>>>>> It is not clear to me why this change was first added. Are we missing 
> >>>>>>> any feature when reverting it?
> >>>>>> This feature was added when we backported the code from Linux to fix 
> >>>>>> the stream match conflict issue
> >>>>>> as part of commit "xen/arm: smmuv1: Intelligent SMR allocation”.
> >>>>>> This is an extra feature added to allocate IOMMU group based on 
> >>>>>> stream-id. If two device has the
> >>>>>> same stream-id then we assign those devices to the same group.
> >>>>> 
> >>>>> If we revert the patch, then it would not be possible to use the SMMU 
> >>>>> if two devices use the same stream-id. Is that correct?
> >>>> No. If we revert the patch we can use the SMMU if two devices use the 
> >>>> same stream-id without any issue but each device will be in a separate 
> >>>> group.This is same behaviour before the code is merged.
> >>> 
> >>> Ok. So there is no change in behavior. Good. Can you propose a commit 
> >>> message clarifying that?
> >> Please have a look if it make sense.
> >> xen/arm: smmuv1: Revert associating the group pointer with the S2CR
> >> Revert the code that associates the group pointer with the S2CR as this
> >> code causing an issue when the SMMU device has more than one master
> >> device with same stream-id. This issue is introduced by the below commit:
> >> “0435784cc75dcfef3b5f59c29deb1dbb84265ddb:xen/arm: smmuv1: Intelligent SMR 
> >> allocation”
> >>  Reverting the code will not impact to use of SMMU if two devices use the
> >> same stream-id but each device will be in a separate group. This is the 
> >> same
> >> behaviour before the code is merged.
> > 
> > Look good to me. Is this patch to be applied on top of Stefano's series? If 
> > not, is there going to be more clash?
> > 
> 
> As per Stefano's mail he already tested his patch series on top of this 
> patch. I think this patch has to merged before Stefano’s patch series 
> Let Stefano also confirm that.
> 
> I think there will be no more clashes.

Yes, this patch is to be committed *before* my series and I have already
tested this patch alone and with my series on top. Both cases work fine.