[PATCH v4 3/3] iommu/arm-smmu-qcom: Implement S2CR quirk

[Bjorn Andersson]

The firmware found in some Qualcomm platforms intercepts writes to S2CR
in order to replace bypass type streams with fault; and ignore S2CR
updates of type fault.

Detect this behavior and implement a custom write_s2cr function in order
to trick the firmware into supporting bypass streams by the means of
configuring the stream for translation using a reserved and disabled
context bank.

Also circumvent the problem of configuring faulting streams by
configuring the stream as bypass.

Signed-off-by: Bjorn Andersson <bjorn.andersson at linaro.org>
---

Changes since v3:
- Move the reservation of the "identity context bank" to the Qualcomm specific
  implementation.
- Implement the S2CR quirk with the newly introduced write_s2cr callback.

 drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c | 68 ++++++++++++++++++++++
 1 file changed, 68 insertions(+)

diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
index 0089048342dd..c0f42d6a6e01 100644
--- a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
+++ b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
@@ -10,8 +10,14 @@
 
 struct qcom_smmu {
 	struct arm_smmu_device smmu;
+	bool bypass_cbndx;
 };
 
+static struct qcom_smmu *to_qcom_smmu(struct arm_smmu_device *smmu)
+{
+	return container_of(smmu, struct qcom_smmu, smmu);
+}
+
 static const struct of_device_id qcom_smmu_client_of_match[] __maybe_unused = {
 	{ .compatible = "qcom,adreno" },
 	{ .compatible = "qcom,mdp4" },
@@ -25,9 +31,32 @@ static const struct of_device_id qcom_smmu_client_of_match[] __maybe_unused = {
 
 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 reg;
 	u32 smr;
 	int 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.
+	 */
+	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);
+	if (FIELD_GET(ARM_SMMU_S2CR_TYPE, reg) != S2CR_TYPE_BYPASS) {
+		qsmmu->bypass_cbndx = smmu->num_context_banks - 1;
+
+		set_bit(qsmmu->bypass_cbndx, smmu->context_map);
+
+		reg = FIELD_PREP(ARM_SMMU_CBAR_TYPE, CBAR_TYPE_S1_TRANS_S2_BYPASS);
+		arm_smmu_gr1_write(smmu, ARM_SMMU_GR1_CBAR(qsmmu->bypass_cbndx), reg);
+	}
+
 	for (i = 0; i < smmu->num_mapping_groups; i++) {
 		smr = arm_smmu_gr0_read(smmu, ARM_SMMU_GR0_SMR(i));
 
@@ -46,6 +75,44 @@ static int qcom_smmu_cfg_probe(struct arm_smmu_device *smmu)
 	return 0;
 }
 
+static void qcom_smmu_write_s2cr(struct arm_smmu_device *smmu, int idx)
+{
+	struct arm_smmu_s2cr *s2cr = smmu->s2crs + idx;
+	struct qcom_smmu *qsmmu = to_qcom_smmu(smmu);
+	u32 cbndx = s2cr->cbndx;
+	u32 type = s2cr->type;
+	u32 reg;
+
+	if (qsmmu->bypass_cbndx) {
+		if (type == S2CR_TYPE_BYPASS) {
+			/*
+			 * Firmware with quirky S2CR handling will substitute
+			 * BYPASS writes with FAULT, so point the stream to the
+			 * reserved context bank and ask for translation on the
+			 * stream
+			 */
+			type = S2CR_TYPE_TRANS;
+			cbndx = qsmmu->bypass_cbndx;
+		} else if (type == S2CR_TYPE_FAULT) {
+			/*
+			 * Firmware with quirky S2CR handling will ignore FAULT
+			 * writes, so trick it to write FAULT by asking for a
+			 * BYPASS.
+			 */
+			type = S2CR_TYPE_BYPASS;
+			cbndx = 0xff;
+		}
+	}
+
+	reg = FIELD_PREP(ARM_SMMU_S2CR_TYPE, type) |
+	      FIELD_PREP(ARM_SMMU_S2CR_CBNDX, cbndx) |
+	      FIELD_PREP(ARM_SMMU_S2CR_PRIVCFG, s2cr->privcfg);
+
+	if (smmu->features & ARM_SMMU_FEAT_EXIDS && smmu->smrs && smmu->smrs[idx].valid)
+		reg |= ARM_SMMU_S2CR_EXIDVALID;
+	arm_smmu_gr0_write(smmu, ARM_SMMU_GR0_S2CR(idx), reg);
+}
+
 static int qcom_smmu_def_domain_type(struct device *dev)
 {
 	const struct of_device_id *match =
@@ -87,6 +154,7 @@ static const struct arm_smmu_impl qcom_smmu_impl = {
 	.cfg_probe = qcom_smmu_cfg_probe,
 	.def_domain_type = qcom_smmu_def_domain_type,
 	.reset = qcom_smmu500_reset,
+	.write_s2cr = qcom_smmu_write_s2cr,
 };
 
 struct arm_smmu_device *qcom_smmu_impl_init(struct arm_smmu_device *smmu)
-- 
2.28.0