[PATCH v3 3/4] iommu/arm-smmu-v3: Add support for dirty tracking in domain alloc

[Tian, Kevin]

> From: Shameerali Kolothum Thodi
> <shameerali.kolothum.thodi at huawei.com>
> 
> > -----Original Message-----
> > From: Tian, Kevin <kevin.tian at intel.com>
> > Sent: Wednesday, May 22, 2024 8:16 AM
> > To: Shameerali Kolothum Thodi
> <shameerali.kolothum.thodi at huawei.com>;
> > iommu at lists.linux.dev; linux-arm-kernel at lists.infradead.org
> > Cc: robin.murphy at arm.com; will at kernel.org; joro at 8bytes.org;
> > jgg at nvidia.com; ryan.roberts at arm.com; nicolinc at nvidia.com;
> > mshavit at google.com; eric.auger at redhat.com;
> joao.m.martins at oracle.com;
> > jiangkunkun <jiangkunkun at huawei.com>; zhukeqian
> > <zhukeqian1 at huawei.com>; Linuxarm <linuxarm at huawei.com>
> > Subject: RE: [PATCH v3 3/4] iommu/arm-smmu-v3: Add support for dirty
> tracking
> > in domain alloc
> >
> > > From: Shameer Kolothum <shameerali.kolothum.thodi at huawei.com>
> > > Sent: Tuesday, April 30, 2024 9:43 PM
> > >
> > > @@ -2422,31 +2425,32 @@ static int arm_smmu_domain_finalise(struct
> > > arm_smmu_domain *smmu_domain,
> > >  	if (!(smmu->features & ARM_SMMU_FEAT_TRANS_S2))
> > >  		smmu_domain->stage = ARM_SMMU_DOMAIN_S1;
> > >
> > > +	pgtbl_cfg = (struct io_pgtable_cfg) {
> > > +		.pgsize_bitmap	= smmu->pgsize_bitmap,
> > > +		.coherent_walk	= smmu->features &
> > > ARM_SMMU_FEAT_COHERENCY,
> > > +		.tlb		= &arm_smmu_flush_ops,
> > > +		.iommu_dev	= smmu->dev,
> > > +	};
> > > +
> > >  	switch (smmu_domain->stage) {
> > >  	case ARM_SMMU_DOMAIN_S1:
> > > -		ias = (smmu->features & ARM_SMMU_FEAT_VAX) ? 52 : 48;
> > > -		ias = min_t(unsigned long, ias, VA_BITS);
> > > -		oas = smmu->ias;
> > > +		unsigned long ias = (smmu->features &
> > > +				     ARM_SMMU_FEAT_VAX) ? 52 : 48;
> > > +		pgtbl_cfg.ias = min_t(unsigned long, ias, VA_BITS);
> > > +		pgtbl_cfg.oas = smmu->ias;
> > > +		if (enable_dirty)
> > > +			pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_ARM_HD;
> >
> > why is dirty tracking considered as a quirk?
> 
> Yes, that is a bit unconventional. But this was discussed earlier and in
> SMMUv3
> driver the word "quirk" is considered in the broadest sense and there are
> precedent for this in the driver already.
> 
> From Robin:
> 
> "Indeed these features aren't decorative grooves on a piece of furniture,
> but in the case of io-pgtable we're merely using "quirk" in its broadest
> sense to imply something that differs from the baseline default
> behaviour - ARM_MTK_EXT, ARM_TTBR1 and ARM_OUTER_WBWA (or
> whatever it's
> called this week) are all just indicating extra hardware features
> entirely comparable to HTTU;..."
> 
> https://lore.kernel.org/linux-iommu/5ada4a8b-8852-f83c-040a-
> 9ef5dac51de2 at arm.com/
> 

I see.