drm/msm: Fix display fault handling

It turns out that when the display is enabled by the bootloader, we can
get some transient iommu faults from the display.  Which doesn't go over
too well when we install a fault handler that is gpu specific.  To avoid
this, defer installing the fault handler until we get around to setting
up per-process pgtables (which is adreno_smmu specific).  The arm-smmu
fallback error reporting is sufficient for reporting display related
faults (and in fact was all we had prior to f8f934c1)
Reported-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reported-by: Yassine Oudjana <y.oudjana@protonmail.com>
Fixes: 2a574cc0 ("drm/msm: Improve the a6xx page fault handler")
Signed-off-by: Rob Clark <robdclark@chromium.org>
Tested-by: John Stultz <john.stultz@linaro.org>
Tested-by: Yassine Oudjana <y.oudjana@protonmail.com>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20210707180113.840741-1-robdclark@gmail.comSigned-off-by: Rob Clark <robdclark@chromium.org>

drivers/gpu/drm/msm/msm_iommu.c

@@ -142,6 +142,9 @@ static const struct iommu_flush_ops null_tlb_ops = {
 	.tlb_add_page = msm_iommu_tlb_add_page,
 };
 
+static int msm_fault_handler(struct iommu_domain *domain, struct device *dev,
+		unsigned long iova, int flags, void *arg);
+
 struct msm_mmu *msm_iommu_pagetable_create(struct msm_mmu *parent)
 {
 	struct adreno_smmu_priv *adreno_smmu = dev_get_drvdata(parent->dev);
@@ -157,6 +160,13 @@ struct msm_mmu *msm_iommu_pagetable_create(struct msm_mmu *parent)
 	if (!ttbr1_cfg)
 		return ERR_PTR(-ENODEV);
 
+	/*
+	 * Defer setting the fault handler until we have a valid adreno_smmu
+	 * to avoid accidentially installing a GPU specific fault handler for
+	 * the display's iommu
+	 */
+	iommu_set_fault_handler(iommu->domain, msm_fault_handler, iommu);
+
 	pagetable = kzalloc(sizeof(*pagetable), GFP_KERNEL);
 	if (!pagetable)
 		return ERR_PTR(-ENOMEM);
@@ -300,7 +310,6 @@ struct msm_mmu *msm_iommu_new(struct device *dev, struct iommu_domain *domain)
 
 	iommu->domain = domain;
 	msm_mmu_init(&iommu->base, dev, &funcs, MSM_MMU_IOMMU);
-	iommu_set_fault_handler(domain, msm_fault_handler, iommu);
 
 	atomic_set(&iommu->pagetables, 0);