Re: [XEN PATCH 10/10] arm/smmu: address violation of MISRA C:2012 Rule 8.2

[Rahul Singh <Rahul.Singh@xxxxxxx>]

Hi Bertrand

> On 16 Oct 2023, at 2:31 pm, Bertrand Marquis <bertrand.marquis@xxxxxxx> wrote:
> 
> Hi Julien,
> 
>> On 16 Oct 2023, at 11:07, Julien Grall <julien@xxxxxxx> wrote:
>> 
>> Hi,
>> 
>> On 13/10/2023 16:24, Federico Serafini wrote:
>>> Add missing parameter names, no functional change.
>>> Signed-off-by: Federico Serafini <federico.serafini@xxxxxxxxxxx>
>>> ---
>>> xen/drivers/passthrough/arm/smmu.c | 6 +++---
>> 
>> This file is using the Linux coding style because it is imported from Linux. 
>> I was under the impression we would exclude such file for now.
>> 
>> Looking at exclude-list.json, it doesn't seem to be present. I think this 
>> patch should be replaced with adding a line in execlude-list.json.
> 
> I think that during one of the discussions we said that this file already 
> deviated quite a lot from the status in Linux and we wanted to turn it to Xen 
> coding style in the future hence it is not listed in the exclude file.
> At the end having a working smmu might be critical in a safety context so it 
> will make sense to also check this part of xen.
> 
> @Rahul: do you agree ?

Yes, you are right current SMMUv3 code already deviates quite a lot from the 
status of Linux
because Xen handles the command queue in a different way than the way Linux 
handles it. 
More detailed can be found at the start of the SMMUv3 file. I am pasting it 
here also.

* 5. Latest version of the Linux SMMUv3 code implements the commands queue
* access functions based on atomic operations implemented in Linux.
* Atomic functions used by the commands queue access functions are not
* implemented in XEN therefore we decided to port the earlier version
* of the code. Atomic operations are introduced to fix the bottleneck of
* the SMMU command queue insertion operation. A new algorithm for
* inserting commands into the queue is introduced, which is
* lock-free on the fast-path.
* Consequence of reverting the patch is that the command queue insertion
* will be slow for large systems as spinlock will be used to serializes
* accesses from all CPUs to the single queue supported by the hardware.
* Once the proper atomic operations will be available in XEN the driver
* can be updated.
 
Anyway because of above reason backporting SMMUv3 Linux driver patches to Xen 
are
not straight forward. If making smmu-v3.c to Xen coding style helps in safety 
context I am okay
with that.

Regards,
Rahul