Re: [PATCH 0/5] Qcom smmu-500 TLB invalidation errata for sdm845

[Vivek Gautam]

On 8/14/2018 5:54 PM, Vivek Gautam wrote:
> Hi Will,
>
>
> On 8/14/2018 5:10 PM, Will Deacon wrote:
> > Hi Vivek,
> >
> > On Tue, Aug 14, 2018 at 04:25:23PM +0530, Vivek Gautam wrote:
> > > Qcom's implementation of arm,mmu-500 on sdm845 has a 
> > > functional/performance
> > > errata [1] because of which the TCU cache look ups are stalled during
> > > invalidation cycle. This is mitigated by serializing all the 
> > > invalidation
> > > requests coming to the smmu.
> > How does this implementation differ from the one supported by 
> > qcom_iommu.c?
> > I notice you're adding firmware hooks here, which we avoided by 
> > having the
> > extra driver. Please help me understand which devices exist, how they
> > differ, and which drivers are intended to support them!
>
> IIRC, the qcom_iommu driver was intended to support the static context 
> bank - SID
> mapping, and is very specific to the smmu-v2 version present on 
> msm8916 soc.
> However, this is the qcom's mmu-500 implementation specific errata. 
> qcom_iommu
> will not be able to support mmu-500 configurations.
> Rob Clark can add more.
> Let you know what you suggest.

Rob, can you please comment about how qcom-smmu driver has different 
implementation
from arm-smmu driver?
Will, in case we would want to use arm-smmu driver, what would you 
suggest for
having the firmware hooks?
Thanks.

Best regards
Vivek
> > Also -- you didn't CC all the maintainers for the firmware bits, so 
> > adding
> > Andy here for that, and Rob for the previous question.
>
> I added Andy to the series, would you want me to add Rob H also?
>
> Best regards
> Vivek
>
> > Thanks,
> >
> > Will