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

[Julien Grall <julien@xen.org>]

Hi,

On 19/04/2021 17:21, Stefano Stabellini wrote:
> On Mon, 19 Apr 2021, Rahul Singh wrote:
>> Hi Julien,
>>
>>> On 18 Apr 2021, at 6:48 pm, Julien Grall <julien@xen.org> 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@xen.org> wrote:
>>>>>
>>>>>
>>>>>
>>>>> On 16/04/2021 17:05, Rahul Singh wrote:
>>>>>>> On 16 Apr 2021, at 4:23 pm, Julien Grall <julien@xen.org> 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@xen.org> 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.

Cool. Thanks for the confirmation. I have committed the patch with the 
new commit message (although, I tweaked a little bit to use the 
abbreviated version of the commit ID).

Cheers,

-- 
Julien Grall