Re: [BUG]SMMU-V3 queue need no-cache memory

[sisyphean <sisyphean@zlw.email>]

Hi Rahul Singh,

在 2022/12/7 18:24, Rahul Singh 写道:
> Hi Sisyphean,
>
> > On 7 Dec 2022, at 2:04 am, sisyphean <sisyphean@zlw.email> wrote:
> >
> > Hi,
> >
> >      I try to run XEN on my ARM board(Sorry, for some commercial reasons, I 
> > can't tell you
> >      on which platform I run XEN)  and enable SMMU-V3, but all cmds in cmdq 
> > failed when XEN started.
> >
> >      After using the debugger to track debugging, the reason for this problem 
> > is that
> >      the queue in the smmu-v3 driver is not no-cache, so after the function 
> > arm_smmu_cmdq_build_cmd
> >      is executed, the cmd is still in cache.Therefore, the SMMU-V3 hardware 
> > cannot obtain the correct cmd
> >      from the memory for execution.
> Yes you are right as of now we are allocating the memory for cmdqueue via 
> _xzalloc() which is cached
> memory because of that you are observing the issue. We have tested the Xen 
> SMMUv3 driver on SOC
> where SMMUv3 HW is in the coherency domain, and because of that we have not 
> encountered this issue.
>
> I think In your case SMMUv3 HW is not in the coherency domain. Please confirm 
> from your side if the
> "dma-coherent” property is not set in DT.
>
> I think there is no function available as of now to request Xen to allocate 
> memory that is not cached.
>
> @Julien and @Stefano do you have any suggestion on how we can request memory 
> from Xen that is not
> cached something like dma_alloc_coherent() in Linux.
>
> Regards,
> Rahul
I have tried to set "dma-coherent" and not set "dma-coherent" in DT. The 
results are consistent, and
SMMUv3 HW cannot get the correct cmd from memory