[PATCH 2/5] iommu/arm-smmu: Emulate bypass by using context banks

Bjorn Andersson
2020-07-09T05:02:04Z

Some firmware found on various Qualcomm platforms traps writes to S2CR
of type BYPASS and writes FAULT into the register. This prevents us from
marking the streams for the display controller as BYPASS to allow
continued scanout of the screen through the initialization of the ARM
SMMU.

This adds a Qualcomm specific cfg_probe function, which probes the
behavior of the S2CR registers and if found faulty enables the related
quirk. Based on this quirk context banks are allocated for IDENTITY
domains as well, but with ARM_SMMU_SCTLR_M omitted.

The result is valid stream mappings, without translation.

Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
---
drivers/iommu/arm-smmu-qcom.c | 21 +++++++++++++++++++++
drivers/iommu/arm-smmu.c | 14 ++++++++++++--
drivers/iommu/arm-smmu.h | 3 +++
3 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/arm-smmu-qcom.c b/drivers/iommu/arm-smmu-qcom.c
index cf01d0215a39..e8a36054e912 100644
--- a/drivers/iommu/arm-smmu-qcom.c
+++ b/drivers/iommu/arm-smmu-qcom.c
@@ -23,6 +23,26 @@ static const struct of_device_id qcom_smmu_client_of_match[] = {
{ }
};

+static int qcom_smmu_cfg_probe(struct arm_smmu_device *smmu)
+{
+ unsigned int last_s2cr = ARM_SMMU_GR0_S2CR(smmu->num_mapping_groups - 1);
+ u32 reg;
+
+ /*
+ * With some firmware writes to S2CR of type FAULT are ignored, and
+ * writing BYPASS will end up as FAULT in the register. Perform a write
+ * to S2CR to detect if this is the case with the current firmware.
+ */
+ arm_smmu_gr0_write(smmu, last_s2cr, 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));
+ reg = arm_smmu_gr0_read(smmu, last_s2cr);
+ if (FIELD_GET(ARM_SMMU_S2CR_TYPE, reg) != S2CR_TYPE_BYPASS)
+ smmu->qcom_bypass_quirk = true;
+
+ return 0;
+}
+
static int qcom_smmu_def_domain_type(struct device *dev)
{
const struct of_device_id *match =
@@ -61,6 +81,7 @@ static int qcom_smmu500_reset(struct arm_smmu_device *smmu)
}

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,
};
diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
index 2e27cf9815ab..f33eda3117fa 100644
--- a/drivers/iommu/arm-smmu.c
+++ b/drivers/iommu/arm-smmu.c
@@ -654,7 +654,9 @@ static 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))
@@ -678,7 +680,11 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
if (smmu_domain->smmu)
goto out_unlock;

- if (domain->type == IOMMU_DOMAIN_IDENTITY) {
+ /*
+ * Nothing to do for IDENTITY domains,unless disabled context banks are
+ * used to emulate bypass mappings on Qualcomm platforms.
+ */
+ if (domain->type == IOMMU_DOMAIN_IDENTITY && !smmu->qcom_bypass_quirk) {
smmu_domain->stage = ARM_SMMU_DOMAIN_BYPASS;
smmu_domain->smmu = smmu;
goto out_unlock;
@@ -826,6 +832,10 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
domain->geometry.aperture_end = (1UL << ias) - 1;
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-smmu.h b/drivers/iommu/arm-smmu.h
index d172c024be61..a71d193073e4 100644
--- a/drivers/iommu/arm-smmu.h
+++ b/drivers/iommu/arm-smmu.h
@@ -305,6 +305,8 @@ struct arm_smmu_device {

/* IOMMU core code handle */
struct iommu_device iommu;
+
+ bool qcom_bypass_quirk;
};

enum arm_smmu_context_fmt {
@@ -323,6 +325,7 @@ struct arm_smmu_cfg {
};
enum arm_smmu_cbar_type cbar;
enum arm_smmu_context_fmt fmt;
+ bool m;
};
#define ARM_SMMU_INVALID_IRPTNDX 0xff

--
2.26.2