[PATCH] iommu/arm-smmu-qcom: Rework the logic finding the bypass quirk

[Manivannan Sadhasivam]

The logic used to find the quirky firmware that intercepts the writes to
S2CR register to replace bypass type streams with a fault, and ignore the
fault type, is not working with the firmware on newer SoCs like SC8280XP.

The current logic uses the last stream mapping group (num_mapping_groups
- 1) as an index for finding quirky firmware. But on SC8280XP, this
logic is not working as the number of stream mapping groups reported by
the SMMU (163 as on the SC8280XP-CRD device) is not valid for some reason.
So the current logic that checks the (163-1) S2CR entry fails to detect
the quirky firmware on these devices and triggers invalid context fault
for bypass streams.

To fix this issue, rework the logic to find the first non-valid (free)
stream mapping register group (SMR) and use that index to access S2CR
for detecting the bypass quirk.

This also warrants a change in variable name from last_s2cr to free_s2cr.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam at linaro.org>
---
 drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c | 24 +++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
index 78fc0e1bf215..4104f81b8d8f 100644
--- a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
+++ b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
@@ -267,23 +267,37 @@ static int qcom_smmu_init_context(struct arm_smmu_domain *smmu_domain,
 
 static int qcom_smmu_cfg_probe(struct arm_smmu_device *smmu)
 {
-	unsigned int last_s2cr = ARM_SMMU_GR0_S2CR(smmu->num_mapping_groups - 1);
 	struct qcom_smmu *qsmmu = to_qcom_smmu(smmu);
+	u32 free_s2cr;
 	u32 reg;
 	u32 smr;
 	int i;
 
+	/*
+	 * Find the first non-valid (free) stream mapping register group and
+	 * use that index to access S2CR for detecting the bypass quirk.
+	 */
+	for (i = 0; i < smmu->num_mapping_groups; i++) {
+		smr = arm_smmu_gr0_read(smmu, ARM_SMMU_GR0_SMR(i));
+
+		if (!FIELD_GET(ARM_SMMU_SMR_VALID, smr))
+			break;
+	}
+
+	free_s2cr = ARM_SMMU_GR0_S2CR(i);
+
 	/*
 	 * With some firmware versions writes to S2CR of type FAULT are
 	 * ignored, and writing BYPASS will end up written as FAULT in the
-	 * register. Perform a write to S2CR to detect if this is the case and
-	 * if so reserve a context bank to emulate bypass streams.
+	 * register. Perform a write to the first free S2CR to detect if
+	 * this is the case and if so reserve a context bank to emulate
+	 * bypass streams.
 	 */
 	reg = FIELD_PREP(ARM_SMMU_S2CR_TYPE, S2CR_TYPE_BYPASS) |
 	      FIELD_PREP(ARM_SMMU_S2CR_CBNDX, 0xff) |
 	      FIELD_PREP(ARM_SMMU_S2CR_PRIVCFG, S2CR_PRIVCFG_DEFAULT);
-	arm_smmu_gr0_write(smmu, last_s2cr, reg);
-	reg = arm_smmu_gr0_read(smmu, last_s2cr);
+	arm_smmu_gr0_write(smmu, free_s2cr, reg);
+	reg = arm_smmu_gr0_read(smmu, free_s2cr);
 	if (FIELD_GET(ARM_SMMU_S2CR_TYPE, reg) != S2CR_TYPE_BYPASS) {
 		qsmmu->bypass_quirk = true;
 		qsmmu->bypass_cbndx = smmu->num_context_banks - 1;
-- 
2.25.1