[PATCH v3 3/8] iommu/arm-smmu: Consult context bank allocator for identify domains

[Bjorn Andersson]

For implementations of the ARM SMMU where stream mappings of bypass type
are prohibited identity domains can be implemented by using context
banks with translation disabled.

Postpone the decision to skip allocating a context bank until the
implementation specific context bank allocator has been consulted and if
it decides to use a context bank for the identity map, don't enable
translation (i.e. omit ARM_SMMU_SCTLR_M).

Signed-off-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxx>
---

Changes since v2:
- Tie this to alloc_context_bank rather than carrying a Qualcomm specific quirk
  in the generic code.

 drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c |  4 ++++
 drivers/iommu/arm/arm-smmu/arm-smmu.c      | 23 +++++++++++++++-------
 drivers/iommu/arm/arm-smmu/arm-smmu.h      |  3 +++
 3 files changed, 23 insertions(+), 7 deletions(-)

diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
index 0663d7d26908..229fc8ff8cea 100644
--- a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
+++ b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
@@ -94,8 +94,12 @@ static int qcom_adreno_smmu_alloc_context_bank(struct arm_smmu_domain *smmu_doma
 					       struct arm_smmu_device *smmu,
 					       struct device *dev, int start)
 {
+	struct iommu_domain *domain = &smmu_domain->domain;
 	int count;
 
+	if (domain->type == IOMMU_DOMAIN_IDENTITY)
+		return ARM_SMMU_CBNDX_BYPASS;
+
 	/*
 	 * Assign context bank 0 to the GPU device so the GPU hardware can
 	 * switch pagetables
diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c b/drivers/iommu/arm/arm-smmu/arm-smmu.c
index add2e1807e21..eb5c6ca5c138 100644
--- a/drivers/iommu/arm/arm-smmu/arm-smmu.c
+++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c
@@ -611,7 +611,9 @@ void arm_smmu_write_context_bank(struct arm_smmu_device *smmu, int idx)
 
 	/* SCTLR */
 	reg = ARM_SMMU_SCTLR_CFIE | ARM_SMMU_SCTLR_CFRE | ARM_SMMU_SCTLR_AFE |
-	      ARM_SMMU_SCTLR_TRE | ARM_SMMU_SCTLR_M;
+	      ARM_SMMU_SCTLR_TRE;
+	if (cfg->m)
+		reg |= ARM_SMMU_SCTLR_M;
 	if (stage1)
 		reg |= ARM_SMMU_SCTLR_S1_ASIDPNE;
 	if (IS_ENABLED(CONFIG_CPU_BIG_ENDIAN))
@@ -627,9 +629,14 @@ static int arm_smmu_alloc_context_bank(struct arm_smmu_domain *smmu_domain,
 				       struct arm_smmu_device *smmu,
 				       struct device *dev, unsigned int start)
 {
+	struct iommu_domain *domain = &smmu_domain->domain;
+
 	if (smmu->impl && smmu->impl->alloc_context_bank)
 		return smmu->impl->alloc_context_bank(smmu_domain, smmu, dev, start);
 
+	if (domain->type == IOMMU_DOMAIN_IDENTITY)
+		return ARM_SMMU_CBNDX_BYPASS;
+
 	return __arm_smmu_alloc_bitmap(smmu->context_map, start, smmu->num_context_banks);
 }
 
@@ -653,12 +660,6 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
 	if (smmu_domain->smmu)
 		goto out_unlock;
 
-	if (domain->type == IOMMU_DOMAIN_IDENTITY) {
-		smmu_domain->stage = ARM_SMMU_DOMAIN_BYPASS;
-		smmu_domain->smmu = smmu;
-		goto out_unlock;
-	}
-
 	/*
 	 * Mapping the requested stage onto what we support is surprisingly
 	 * complicated, mainly because the spec allows S1+S2 SMMUs without
@@ -757,6 +758,10 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
 	ret = arm_smmu_alloc_context_bank(smmu_domain, smmu, dev, start);
 	if (ret < 0) {
 		goto out_unlock;
+	} else if (ret == ARM_SMMU_CBNDX_BYPASS) {
+		smmu_domain->stage = ARM_SMMU_DOMAIN_BYPASS;
+		smmu_domain->smmu = smmu;
+		goto out_unlock;
 	}
 
 	smmu_domain->smmu = smmu;
@@ -813,6 +818,10 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
 
 	domain->geometry.force_aperture = true;
 
+	/* Enable translation for non-identity context banks */
+	if (domain->type != IOMMU_DOMAIN_IDENTITY)
+		cfg->m = true;
+
 	/* Initialise the context bank with our page table cfg */
 	arm_smmu_init_context_bank(smmu_domain, &pgtbl_cfg);
 	arm_smmu_write_context_bank(smmu, cfg->cbndx);
diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.h b/drivers/iommu/arm/arm-smmu/arm-smmu.h
index ddf2ca4c923d..235d9a3a6ab6 100644
--- a/drivers/iommu/arm/arm-smmu/arm-smmu.h
+++ b/drivers/iommu/arm/arm-smmu/arm-smmu.h
@@ -243,6 +243,8 @@ enum arm_smmu_cbar_type {
 #define TLB_LOOP_TIMEOUT		1000000	/* 1s! */
 #define TLB_SPIN_COUNT			10
 
+#define ARM_SMMU_CBNDX_BYPASS		0xffff
+
 /* Shared driver definitions */
 enum arm_smmu_arch_version {
 	ARM_SMMU_V1,
@@ -346,6 +348,7 @@ struct arm_smmu_cfg {
 	u32				sctlr_clr;    /* bits to mask in SCTLR */
 	enum arm_smmu_cbar_type		cbar;
 	enum arm_smmu_context_fmt	fmt;
+	bool				m;
 };
 #define ARM_SMMU_INVALID_IRPTNDX	0xff
 
-- 
2.28.0