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

[Julien Grall <julien@xxxxxxx>]

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?
OOI why was the code added if it doesn't make any difference?

Anyway, thanks for the explanation!

Cheers,

--
Julien Grall