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

[Rahul Singh <Rahul.Singh@xxxxxxx>]

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.


Regards,
Rahul

> Cheers,
> 
> -- 
> Julien Grall