Re: [PATCHv3] iommu/arm-smmu: Optimize ->tlb_flush_walk() for qcom implementation

[Sai Prakash Ranjan]

On 2021-08-10 23:38, Will Deacon wrote:
> On Tue, Aug 03, 2021 at 11:09:17AM +0530, Sai Prakash Ranjan wrote:
> > On 2021-08-02 21:13, Will Deacon wrote:
> > > On Wed, Jun 23, 2021 at 07:12:01PM +0530, Sai Prakash Ranjan wrote:
> > > > diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c
> > > > b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> > > > index d3c6f54110a5..f3845e822565 100644
> > > > --- a/drivers/iommu/arm/arm-smmu/arm-smmu.c
> > > > +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> > > > @@ -341,6 +341,12 @@ static void arm_smmu_tlb_add_page_s1(struct
> > > > iommu_iotlb_gather *gather,
> > > >  				  ARM_SMMU_CB_S1_TLBIVAL);
> > > >  }
> > > >
> > > > +static void arm_smmu_tlb_inv_walk_impl_s1(unsigned long iova,
> > > > size_t size,
> > > > +				     size_t granule, void *cookie)
> > > > +{
> > > > +	arm_smmu_tlb_inv_context_s1(cookie);
> > > > +}
> > > > +
> > > >  static void arm_smmu_tlb_inv_walk_s2(unsigned long iova, size_t size,
> > > >  				     size_t granule, void *cookie)
> > > >  {
> > > > @@ -388,6 +394,12 @@ static const struct iommu_flush_ops
> > > > arm_smmu_s1_tlb_ops = {
> > > >  	.tlb_add_page	= arm_smmu_tlb_add_page_s1,
> > > >  };
> > > >
> > > > +const struct iommu_flush_ops arm_smmu_s1_tlb_impl_ops = {
> > > > +	.tlb_flush_all	= arm_smmu_tlb_inv_context_s1,
> > > > +	.tlb_flush_walk	= arm_smmu_tlb_inv_walk_impl_s1,
> > > > +	.tlb_add_page	= arm_smmu_tlb_add_page_s1,
> > > > +};
> > >
> > > Hmm, dunno about this. Wouldn't it be a lot cleaner if the
> > > tlb_flush_walk
> > > callbacks just did the right thing based on the smmu_domain (maybe in
> > > the
> > > arm_smmu_cfg?) rather than having an entirely new set of ops just
> > > because
> > > they're const and you can't overide the bit you want?
> > >
> > > I don't think there's really an awful lot qcom-specific about the
> > > principle
> > > here -- there's a trade-off between over-invalidation and invalidation
> > > latency. That happens on the CPU as well.
> > >
> >
> > Sorry didn't understand, based on smmu_domain what? How do we make
> > this implementation specific? Do you mean something like a quirk?
> > The reason we didn't make this common was because nvidia folks weren't
> > so happy with that, you can find the discussion in this thread [1].
> >
> > [1] 
> > https://lore.kernel.org/lkml/20210609145315.25750-1-saiprakash.ranjan@xxxxxxxxxxxxxx/
>
> The ->tlb_flush_walk() callbacks take a 'void *cookie' which, for this
> driver, is a 'struct arm_smmu_domain *'. From that, you can get to the
> 'struct arm_smmu_cfg' which could have something as coarse as:
>
> 	bool	flush_walk_prefer_tlbiasid;
>
> which you can set when you initialise the domain (maybe in the
> ->init_context callback?). It shouldn't affect anybody else.

Ah ok, you meant a new flag in arm_smmu_cfg, right getting it from 
cookie
is no big deal but nonetheless thanks for detailing it. I have made the
changes and sent a v4 after testing.

Thanks,
Sai

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