Re: [PATCH v2 1/3] iommu/arm-smmu: introduction of ACTLR for custom prefetcher settings

[Robin Murphy <robin.murphy@xxxxxxx>]

On 2023-11-15 1:54 pm, Bibek Kumar Patro wrote:
> > > @@ -467,6 +505,9 @@ static struct arm_smmu_device 
> > > *qcom_smmu_create(struct arm_smmu_device *smmu,
> > >       qsmmu->smmu.impl = impl;
> > >       qsmmu->cfg = data->cfg;
> > >
> > > +    if (data->actlrcfg && (data->actlrcfg->size))
> > > +        qsmmu->actlrcfg = data->actlrcfg;
> >
> > Do we really need to replicate multiple parts of the data, or would it 
> > be sensible to just replace qsmmu->cfg with qsmmu->data and handle the 
> > further dereferences in the places that want them?
>
> Mm, could not understand this properly. :( Could you help explain more 
> please?
> As per my understanding aren't data and qsmmu different structures.
> qcom_smmu is a superset of arm_smmu housing additonal properties
> and qcom_smmu_match_data is kind of a superset of arm_smmu_impl with
> additional specific implmentations, so both needs to be in place?
> Apologies if I understood your statement incorrectly.

My point is that the data is static and constant, so there's really no 
point storing multiple pointers into different bits of it. So rather than:

	qsmmu->cfg = data->cfg;
	qssmu->actlrcfg = data->actlrcfg;
	...
	do_something(qsmmu->cfg);
	...
	do_other_thing(qsmmu->actlrcfg);

we can just store the one pointer and have:

	qsmmu->data = data;
	...
	do_something(qsmmu->data->cfg);
	...
	do_other_thing(qsmmu->data->actlrcfg);

Thanks,
Robin.

> > > +
> > >       return &qsmmu->smmu;
> > >   }
> > >
> > > diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.h 
> > > b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.h
> > > index 593910567b88..4b6862715070 100644
> > > --- a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.h
> > > +++ b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.h
> > > @@ -9,6 +9,7 @@
> > >   struct qcom_smmu {
> > >       struct arm_smmu_device smmu;
> > >       const struct qcom_smmu_config *cfg;
> > > +    const struct actlr_config *actlrcfg;
> > >       bool bypass_quirk;
> > >       u8 bypass_cbndx;
> > >       u32 stall_enabled;
> > > @@ -25,6 +26,7 @@ struct qcom_smmu_config {
> > >   };