[PATCH] iommu/arm-smmu: Improve SMR mask test

* [PATCH] iommu/arm-smmu: Improve SMR mask test
@ 2020-01-10 15:25 ` Robin Murphy
  0 siblings, 0 replies; 2+ messages in thread
From: Robin Murphy @ 2020-01-10 15:25 UTC (permalink / raw)
  To: will; +Cc: iommu, linux-arm-kernel

Make the SMR mask test more robust against SMR0 being live
at probe time, which might happen once we start supporting
firmware reservations for framebuffers and suchlike.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
 drivers/iommu/arm-smmu.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
index 4f1a350d9529..df6490bc7700 100644
--- a/drivers/iommu/arm-smmu.c
+++ b/drivers/iommu/arm-smmu.c
@@ -946,23 +946,36 @@ static void arm_smmu_write_sme(struct arm_smmu_device *smmu, int idx)
 static void arm_smmu_test_smr_masks(struct arm_smmu_device *smmu)
 {
 	u32 smr;
+	int i;
 
 	if (!smmu->smrs)
 		return;
-
+	/*
+	 * If we've had to accommodate firmware memory regions, we may
+	 * have live SMRs by now; tread carefully...
+	 *
+	 * Somewhat perversely, not having a free SMR for this test implies we
+	 * can get away without it anyway, as we'll only be able to 'allocate'
+	 * these SMRs for the ID/mask values we're already trusting to be OK.
+	 */
+	for (i = 0; i < smmu->num_mapping_groups; i++)
+		if (!smmu->smrs[i].valid)
+			goto smr_ok;
+	return;
+smr_ok:
 	/*
 	 * 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 = FIELD_PREP(SMR_ID, smmu->streamid_mask);
-	arm_smmu_gr0_write(smmu, ARM_SMMU_GR0_SMR(0), smr);
-	smr = arm_smmu_gr0_read(smmu, ARM_SMMU_GR0_SMR(0));
+	arm_smmu_gr0_write(smmu, ARM_SMMU_GR0_SMR(i), smr);
+	smr = arm_smmu_gr0_read(smmu, ARM_SMMU_GR0_SMR(i));
 	smmu->streamid_mask = FIELD_GET(SMR_ID, smr);
 
 	smr = FIELD_PREP(SMR_MASK, smmu->streamid_mask);
-	arm_smmu_gr0_write(smmu, ARM_SMMU_GR0_SMR(0), smr);
-	smr = arm_smmu_gr0_read(smmu, ARM_SMMU_GR0_SMR(0));
+	arm_smmu_gr0_write(smmu, ARM_SMMU_GR0_SMR(i), smr);
+	smr = arm_smmu_gr0_read(smmu, ARM_SMMU_GR0_SMR(i));
 	smmu->smr_mask_mask = FIELD_GET(SMR_MASK, smr);
 }
 
-- 
2.23.0.dirty

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