Re: [PATCH v7 5/6] iommu/arm-smmu-v3: Add support for non-strict mode

[Robin Murphy]

On 2018-09-18 6:10 PM, Will Deacon wrote:
> On Fri, Sep 14, 2018 at 03:30:23PM +0100, Robin Murphy wrote:
> > From: Zhen Lei <thunder.leizhen@xxxxxxxxxx>
> >
> > Dynamically choose strict or non-strict mode for page table config based
> > on the iommu domain type.
>
> It's the domain type in conjunction with the attribute that determines
> whether we use lazy or strict invalidation.
>
> > Signed-off-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx>
> > [rm: convert to domain attribute]
> > Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>
> > ---
> >   drivers/iommu/arm-smmu-v3.c | 30 ++++++++++++++++++++++++------
> >   1 file changed, 24 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
> > index f10c852479fc..7bbfa5f7ce8e 100644
> > --- a/drivers/iommu/arm-smmu-v3.c
> > +++ b/drivers/iommu/arm-smmu-v3.c
> > @@ -612,6 +612,7 @@ struct arm_smmu_domain {
> >   	struct mutex			init_mutex; /* Protects smmu pointer */
> >   
> >   	struct io_pgtable_ops		*pgtbl_ops;
> > +	bool				non_strict;
> >   
> >   	enum arm_smmu_domain_stage	stage;
> >   	union {
> > @@ -1633,6 +1634,9 @@ static int arm_smmu_domain_finalise(struct iommu_domain *domain)
> >   	if (smmu->features & ARM_SMMU_FEAT_COHERENCY)
> >   		pgtbl_cfg.quirks = IO_PGTABLE_QUIRK_NO_DMA;
> >   
> > +	if (smmu_domain->non_strict)
> > +		pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_NON_STRICT;
> > +
> >   	pgtbl_ops = alloc_io_pgtable_ops(fmt, &pgtbl_cfg, smmu_domain);
> >   	if (!pgtbl_ops)
> >   		return -ENOMEM;
> > @@ -1934,13 +1938,17 @@ static int arm_smmu_domain_get_attr(struct iommu_domain *domain,
> >   {
> >   	struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
> >   
> > -	if (domain->type != IOMMU_DOMAIN_UNMANAGED)
> > -		return -EINVAL;
> > -
> >   	switch (attr) {
> >   	case DOMAIN_ATTR_NESTING:
> > +		if (domain->type != IOMMU_DOMAIN_UNMANAGED)
> > +			return -EINVAL;
> >   		*(int *)data = (smmu_domain->stage == ARM_SMMU_DOMAIN_NESTED);
> >   		return 0;
> > +	case DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE:
> > +		if (domain->type != IOMMU_DOMAIN_DMA)
> > +			return -EINVAL;
> > +		*(int *)data = smmu_domain->non_strict;
> > +		return 0;
> >   	default:
> >   		return -ENODEV;
>
> Hmm, there's a change in behaviour here (and also in the set function)
> which is that unknown attributes now return -ENODEV for managed domains
> instead of -EINVAL. I don't know if that's a problem, but I'd be inclined
> to switch on the domain type and then have a nested switch for the supported
> attributes.

Sure, a nested switch did actually cross my mind, but I was worried it 
might be a little boilerplate-heavy since there's still only one of each 
case (and this quick'n'dirty copy-paste job didn't need any thought...)

If that's your preference too, though, I'll respin both driver patches 
that way.

Robin.