[RFC 2/2] iommu: arm-smmu: Don't blindly use first SMR to calculate mask

[Bjorn Andersson <bjorn.andersson@xxxxxxxxxx>]

With the SMRs inherited from the bootloader the first SMR might actually
be valid and in use. As such probing the SMR mask using the first SMR
might break a stream in use. Search for an unused stream and use this to
probe the SMR mask.

Signed-off-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxx>
---
 drivers/iommu/arm-smmu.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
index c8629a656b42..0c6f5fe6f382 100644
--- a/drivers/iommu/arm-smmu.c
+++ b/drivers/iommu/arm-smmu.c
@@ -1084,23 +1084,35 @@ static void arm_smmu_test_smr_masks(struct arm_smmu_device *smmu)
 {
 	void __iomem *gr0_base = ARM_SMMU_GR0(smmu);
 	u32 smr;
+	int idx;
 
 	if (!smmu->smrs)
 		return;
 
+	for (idx = 0; idx < smmu->num_mapping_groups; idx++) {
+		smr = readl_relaxed(gr0_base + ARM_SMMU_GR0_SMR(idx));
+		if (!(smr & SMR_VALID))
+			break;
+	}
+
+	if (idx == smmu->num_mapping_groups) {
+		dev_err(smmu->dev, "Unable to compute streamid_mask\n");
+		return;
+	}
+
 	/*
 	 * SMR.ID bits may not be preserved if the corresponding MASK
 	 * bits are set, so check each one separately. We can reject
 	 * masters later if they try to claim IDs outside these masks.
 	 */
 	smr = smmu->streamid_mask << SMR_ID_SHIFT;
-	writel_relaxed(smr, gr0_base + ARM_SMMU_GR0_SMR(0));
-	smr = readl_relaxed(gr0_base + ARM_SMMU_GR0_SMR(0));
+	writel_relaxed(smr, gr0_base + ARM_SMMU_GR0_SMR(idx));
+	smr = readl_relaxed(gr0_base + ARM_SMMU_GR0_SMR(idx));
 	smmu->streamid_mask = smr >> SMR_ID_SHIFT;
 
 	smr = smmu->streamid_mask << SMR_MASK_SHIFT;
-	writel_relaxed(smr, gr0_base + ARM_SMMU_GR0_SMR(0));
-	smr = readl_relaxed(gr0_base + ARM_SMMU_GR0_SMR(0));
+	writel_relaxed(smr, gr0_base + ARM_SMMU_GR0_SMR(idx));
+	smr = readl_relaxed(gr0_base + ARM_SMMU_GR0_SMR(idx));
 	smmu->smr_mask_mask = smr >> SMR_MASK_SHIFT;
 }
 
-- 
2.18.0