Re: [Freedreno] [PATCH v9 4/7] iommu/arm-smmu: Add a pointer to the attached device to smmu_domain

Will Deacon
2020-07-16T08:52:12Z

On Mon, Jul 13, 2020 at 11:19:17AM -0600, Jordan Crouse wrote:
> On Mon, Jul 13, 2020 at 04:09:02PM +0100, Will Deacon wrote:
> > On Fri, Jun 26, 2020 at 02:00:38PM -0600, Jordan Crouse wrote:
> > > diff --git a/drivers/iommu/arm-smmu.h b/drivers/iommu/arm-smmu.h
> > > index 5f2de20e883b..d33cfe26b2f5 100644
> > > --- a/drivers/iommu/arm-smmu.h
> > > +++ b/drivers/iommu/arm-smmu.h
> > > @@ -345,6 +345,7 @@ struct arm_smmu_domain {
> > > struct mutex init_mutex; /* Protects smmu pointer */
> > > spinlock_t cb_lock; /* Serialises ATS1* ops and TLB syncs */
> > > struct iommu_domain domain;
> > > + struct device *dev; /* Device attached to this domain */
> >
> > This really doesn't feel right to me -- you can generally have multiple
> > devices attached to a domain and they can come and go without the domain
> > being destroyed. Perhaps you could instead identify the GPU during
> > cfg_probe() and squirrel that information away somewhere?
>
> I need some help here. The SMMU device (qcom,adreno-smmu) will have at least two
> stream ids from two different platform devices (GPU and GMU) and I need to
> configure split-pagetable and stall/terminate differently on the two domains.

Hmm. How does the GPU driver know which context bank is assigned to the GPU
and which one is assigned to the GMU? I assume it needs this information so
that it can play its nasty tricks with the TTBR registers?

I ask because if we need to guarantee stability of the context-bank
assignment, then you could match on that in the ->init_context() callback,
but now I worry that it currently works by luck :/

Do we need to add an extra callback to allocate the context bank?

Will