[PATCH 4/7] iommu/arm-smmu: Check for num_context_irqs > 0 to avoid divide by zero exception

[Andreas Herrmann]

With the right (or wrong;-) definition of v1 SMMU node in DTB it is
possible to trigger a division by zero in arm_smmu_init_domain_context
(if number of context irqs is 0):

       if (smmu->version == 1) {
               root_cfg->irptndx = atomic_inc_return(&smmu->irptndx);
 →             root_cfg->irptndx %= smmu->num_context_irqs;
       } else {

Avoid this by checking for num_context_irqs > 0 before trying to
assign interrupts to contexts.

Signed-off-by: Andreas Herrmann <andreas.herrmann at calxeda.com>
---
 drivers/iommu/arm-smmu.c |   31 +++++++++++++++++--------------
 1 file changed, 17 insertions(+), 14 deletions(-)

diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
index f5a856e..0dfd255 100644
--- a/drivers/iommu/arm-smmu.c
+++ b/drivers/iommu/arm-smmu.c
@@ -828,21 +828,24 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
 		return ret;
 
 	root_cfg->cbndx = ret;
-	if (smmu->version == 1) {
-		root_cfg->irptndx = atomic_inc_return(&smmu->irptndx);
-		root_cfg->irptndx %= smmu->num_context_irqs;
-	} else {
-		root_cfg->irptndx = root_cfg->cbndx;
-	}
 
-	irq = smmu->irqs[smmu->num_global_irqs + root_cfg->irptndx];
-	ret = request_irq(irq, arm_smmu_context_fault, IRQF_SHARED,
-			  "arm-smmu-context-fault", domain);
-	if (IS_ERR_VALUE(ret)) {
-		dev_err(smmu->dev, "failed to request context IRQ %d (%u)\n",
-			root_cfg->irptndx, irq);
-		root_cfg->irptndx = -1;
-		goto out_free_context;
+	if (smmu->num_context_irqs) {
+		if (smmu->version == 1) {
+			root_cfg->irptndx = atomic_inc_return(&smmu->irptndx);
+			root_cfg->irptndx %= smmu->num_context_irqs;
+		} else {
+			root_cfg->irptndx = root_cfg->cbndx;
+		}
+
+		irq = smmu->irqs[smmu->num_global_irqs + root_cfg->irptndx];
+		ret = request_irq(irq, arm_smmu_context_fault, IRQF_SHARED,
+				"arm-smmu-context-fault", domain);
+		if (IS_ERR_VALUE(ret)) {
+			dev_err(smmu->dev, "failed to request context IRQ %d (%u)\n",
+				root_cfg->irptndx, irq);
+			root_cfg->irptndx = -1;
+			goto out_free_context;
+		}
 	}
 
 	root_cfg->smmu = smmu;
-- 
1.7.9.5