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

On Thu, Jul 16, 2020 at 1:51 AM Will Deacon [off-list ref] wrote:

On Mon, Jul 13, 2020 at 11:19:17AM -0600, Jordan Crouse wrote:

quoted

On Mon, Jul 13, 2020 at 04:09:02PM +0100, Will Deacon wrote:

quoted

On Fri, Jun 26, 2020 at 02:00:38PM -0600, Jordan Crouse wrote:

quoted

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 :/

Yeah, it is basically by luck right now.. some sort of impl callback
which was passed the dev into impl->init_context() might do the trick
(ie. then the impl could match on compat string)

BR,
-R

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

Will
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