[PATCH v17 1/5] iommu/arm-smmu: re-enable context caching in smmu reset operation

[Bibek Kumar Patro]

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.

Add config 'ARM_SMMU_MMU_500_CPRE_ERRATA' to gate this errata
workaround in default MMU-500 reset operation which defaults to
'Y' and provide option to disable workaround for context caching
in prefetch buffer as and when needed.

Suggested-by: Will Deacon <will at kernel.org>
Signed-off-by: Bibek Kumar Patro <quic_bibekkum at quicinc.com>
---
 Documentation/arch/arm64/silicon-errata.rst |  3 ++-
 drivers/iommu/Kconfig                       | 12 ++++++++++++
 drivers/iommu/arm/arm-smmu/arm-smmu-impl.c  |  2 ++
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/Documentation/arch/arm64/silicon-errata.rst b/Documentation/arch/arm64/silicon-errata.rst
index 65bfab1b1861..92207d55fd1c 100644
--- a/Documentation/arch/arm64/silicon-errata.rst
+++ b/Documentation/arch/arm64/silicon-errata.rst
@@ -198,7 +198,8 @@ stable kernels.
 +----------------+-----------------+-----------------+-----------------------------+
 | ARM            | Neoverse-V3     | #3312417        | ARM64_ERRATUM_3194386       |
 +----------------+-----------------+-----------------+-----------------------------+
-| ARM            | MMU-500         | #841119,826419  | N/A                         |
+| ARM            | MMU-500         | #841119,826419  | ARM_SMMU_MMU_500_CPRE_ERRATA|
+|                |                 | #562869,1047329 |                             |
 +----------------+-----------------+-----------------+-----------------------------+
 | ARM            | MMU-600         | #1076982,1209401| N/A                         |
 +----------------+-----------------+-----------------+-----------------------------+
diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
index ade4e8cf2a3e..90ba5818af81 100644
--- a/drivers/iommu/Kconfig
+++ b/drivers/iommu/Kconfig
@@ -367,6 +367,18 @@ config ARM_SMMU_DISABLE_BYPASS_BY_DEFAULT
 	  'arm-smmu.disable_bypass' will continue to override this
 	  config.

+config ARM_SMMU_MMU_500_CPRE_ERRATA
+	bool "Enable errata workaround for CPRE in SMMU reset path"
+	depends on ARM_SMMU
+	default y
+	help
+	  Say Y here (by default) to apply workaround to disable
+	  MMU-500's next-page prefetcher for sake of 4 known errata.
+
+	  Say N here only when it is sure that any errata related to
+	  prefetch enablement are not applicable on the platform.
+	  Refer silicon-errata.rst for info on errata IDs.
+
 config ARM_SMMU_QCOM
 	def_tristate y
 	depends on ARM_SMMU && ARCH_QCOM
diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu-impl.c b/drivers/iommu/arm/arm-smmu/arm-smmu-impl.c
index 99030e6b16e7..632f1667ceb3 100644
--- a/drivers/iommu/arm/arm-smmu/arm-smmu-impl.c
+++ b/drivers/iommu/arm/arm-smmu/arm-smmu-impl.c
@@ -128,6 +128,7 @@ int arm_mmu500_reset(struct arm_smmu_device *smmu)
 	reg |= ARM_MMU500_ACR_SMTNMB_TLBEN | ARM_MMU500_ACR_S2CRB_TLBEN;
 	arm_smmu_gr0_write(smmu, ARM_SMMU_GR0_sACR, reg);

+#ifdef CONFIG_ARM_SMMU_MMU_500_CPRE_ERRATA
 	/*
 	 * Disable MMU-500's not-particularly-beneficial next-page
 	 * prefetcher for the sake of at least 5 known errata.
@@ -140,6 +141,7 @@ int arm_mmu500_reset(struct arm_smmu_device *smmu)
 		if (reg & ARM_MMU500_ACTLR_CPRE)
 			dev_warn_once(smmu->dev, "Failed to disable prefetcher for errata workarounds, check SACR.CACHE_LOCK\n");
 	}
+#endif

 	return 0;
 }
--
2.34.1