Default MMU-500 reset operation disables context caching in
prefetch buffer. It is however expected for context banks using
the ACTLR register to retain their prefetch value during reset
and runtime suspend.

Replace default MMU-500 reset operation with Qualcomm specific reset
operation which envelope the default reset operation and re-enables
context caching in prefetch buffer for Qualcomm SoCs.

Suggested-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Bibek Kumar Patro <quic_bibekkum@quicinc.com>
---
 drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c | 33 ++++++++++++++++++++--
 1 file changed, 30 insertions(+), 3 deletions(-)

diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
index 549ae4dba3a6..225a53486307 100644
--- a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
+++ b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
@@ -14,6 +14,16 @@

 #define QCOM_DUMMY_VAL	-1

+/*
+ * SMMU-500 TRM defines BIT(0) as CMTLB (Enable context caching in the
+ * macro TLB) and BIT(1) as CPRE (Enable context caching in the prefetch
+ * buffer). The remaining bits are implementation defined and vary across
+ * SoCs.
+ */
+
+#define CPRE			(1 << 1)
+#define CMTLB			(1 << 0)
+
 static struct qcom_smmu *to_qcom_smmu(struct arm_smmu_device *smmu)
 {
 	return container_of(smmu, struct qcom_smmu, smmu);
@@ -376,11 +386,28 @@ static int qcom_smmu_def_domain_type(struct device *dev)
 	return match ? IOMMU_DOMAIN_IDENTITY : 0;
 }

+static int qcom_smmu500_reset(struct arm_smmu_device *smmu)
+{
+	u32 val;
+	int i;
+
+	arm_mmu500_reset(smmu);
+
+	/* arm_mmu500_reset() disables CPRE which is re-enabled here */
+	for (i = 0; i < smmu->num_context_banks; ++i) {
+		val = arm_smmu_cb_read(smmu, i, ARM_SMMU_CB_ACTLR);
+		val |= CPRE;
+		arm_smmu_cb_write(smmu, i, ARM_SMMU_CB_ACTLR, val);
+	}
+
+	return 0;
+}
+
 static int qcom_sdm845_smmu500_reset(struct arm_smmu_device *smmu)
 {
 	int ret;

-	arm_mmu500_reset(smmu);
+	qcom_smmu500_reset(smmu);

 	/*
 	 * To address performance degradation in non-real time clients,
@@ -407,7 +434,7 @@ static const struct arm_smmu_impl qcom_smmu_500_impl = {
 	.init_context = qcom_smmu_init_context,
 	.cfg_probe = qcom_smmu_cfg_probe,
 	.def_domain_type = qcom_smmu_def_domain_type,
-	.reset = arm_mmu500_reset,
+	.reset = qcom_smmu500_reset,
 	.write_s2cr = qcom_smmu_write_s2cr,
 	.tlb_sync = qcom_smmu_tlb_sync,
 };
@@ -432,7 +459,7 @@ static const struct arm_smmu_impl qcom_adreno_smmu_v2_impl = {
 static const struct arm_smmu_impl qcom_adreno_smmu_500_impl = {
 	.init_context = qcom_adreno_smmu_init_context,
 	.def_domain_type = qcom_smmu_def_domain_type,
-	.reset = arm_mmu500_reset,
+	.reset = qcom_smmu500_reset,
 	.alloc_context_bank = qcom_adreno_smmu_alloc_context_bank,
 	.write_sctlr = qcom_adreno_smmu_write_sctlr,
 	.tlb_sync = qcom_smmu_tlb_sync,
--
2.17.1

On 19.12.2023 14:59, Bibek Kumar Patro wrote:
> Default MMU-500 reset operation disables context caching in
> prefetch buffer. It is however expected for context banks using
> the ACTLR register to retain their prefetch value during reset
> and runtime suspend.
> 
> Replace default MMU-500 reset operation with Qualcomm specific reset
> operation which envelope the default reset operation and re-enables
> context caching in prefetch buffer for Qualcomm SoCs.
> 
> Suggested-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Suggested-by implies I came up with this being a solution to
an issue.. definitely not the case!

Konrad

On 12/19/2023 11:29 PM, Konrad Dybcio wrote:
> On 19.12.2023 14:59, Bibek Kumar Patro wrote:
>> Default MMU-500 reset operation disables context caching in
>> prefetch buffer. It is however expected for context banks using
>> the ACTLR register to retain their prefetch value during reset
>> and runtime suspend.
>>
>> Replace default MMU-500 reset operation with Qualcomm specific reset
>> operation which envelope the default reset operation and re-enables
>> context caching in prefetch buffer for Qualcomm SoCs.
>>
>> Suggested-by: Konrad Dybcio <konrad.dybcio@linaro.org>
> Suggested-by implies I came up with this being a solution to
> an issue.. definitely not the case!
> 

Noted, will send v6 by removing the Suggested by tag
and will address the return check as well.

Thanks,
Bibek

> Konrad