iommu/arm-smmu: Check for num_context_irqs > 0 to avoid divide by zero exception

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 when probing
for SMMU devices.

Signed-off-by: Andreas Herrmann <andreas.herrmann@calxeda.com>
[will: changed to dev_err on probe failure path]
Signed-off-by: Will Deacon <will.deacon@arm.com>

1 files changed, 4 insertions, 5 deletions

diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
index 1f79daa5f4b1..e4693cee5f2c 100644
--- a/drivers/iommu/arm-smmu.c
+++ b/drivers/iommu/arm-smmu.c
@@ -1798,12 +1798,11 @@ static int arm_smmu_device_dt_probe(struct platform_device *pdev)
                         smmu->num_context_irqs++;
         }
 
-        if (num_irqs < smmu->num_global_irqs) {
-                dev_warn(dev, "found %d interrupts but expected at least %d\n",
-                         num_irqs, smmu->num_global_irqs);
-                smmu->num_global_irqs = num_irqs;
+        if (!smmu->num_context_irqs) {
+                dev_err(dev, "found %d interrupts but expected at least %d\n",
+                        num_irqs, smmu->num_global_irqs + 1);
+                return -ENODEV;
         }
-        smmu->num_context_irqs = num_irqs - smmu->num_global_irqs;
 
         smmu->irqs = devm_kzalloc(dev, sizeof(*smmu->irqs) * num_irqs,
                                   GFP_KERNEL);