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

[Vivek Gautam]

On 9/5/2018 3:34 PM, Rob Clark wrote:
> On Wed, Sep 5, 2018 at 5:22 AM Vivek Gautam <vivek.gautam@xxxxxxxxxxxxxx> wrote:
> > 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?
> sorry, I missed this thread earlier.  But yeah, as you mentioned, the
> purpose for qcom_iommu.c was to deal with the static context/SID
> mapping.
>
> (I guess it is all just software, and we could make qcom_iommu.c
> support dynamic mapping as well, but I think then it starts to
> duplicate most of arm_smmu.c, so that doesn't seem like the right
> direction)

Thanks Rob for the response. I will wait for Will's response on how would he
like this support be implemented.

Best regards
Vivek
> BR,
> -R
>
> > Will, in case we would want to use arm-smmu driver, what would you
> > suggest for
> > having the firmware hooks?
> > Thanks.
> >
> > Best regards
> > Vivek