[PATCH v2 1/1] iommu: Add config option to set lazy mode as default

[Zhen Lei]

This allows the default behaviour to be controlled by a kernel config
option instead of changing the command line for the kernel to include
"iommu.strict=0" on ARM64 where this is desired.

This is similar to CONFIG_IOMMU_DEFAULT_PASSTHROUGH.

Note: At present, intel_iommu, amd_iommu and s390_iommu use lazy mode as
default, so there is no need to add code for them.

Signed-off-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx>
---
 drivers/iommu/Kconfig | 14 ++++++++++++++
 drivers/iommu/iommu.c |  5 +++++
 2 files changed, 19 insertions(+)

diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
index 6f07f3b21816c64..5daa110d0e83a07 100644
--- a/drivers/iommu/Kconfig
+++ b/drivers/iommu/Kconfig
@@ -85,6 +85,20 @@ config IOMMU_DEFAULT_PASSTHROUGH

 	  If unsure, say N here.

+config IOMMU_DMA_DEFAULT_LAZY_MODE
+	bool "IOMMU DMA use lazy mode to flush IOTLB and free IOVA"
+	depends on IOMMU_API
+	help
+	  Support lazy mode, where for every IOMMU DMA unmap operation, the
+	  flush operation of IOTLB and the free operation of IOVA are deferred.
+	  They are only guaranteed to be done before the related IOVA will be
+	  reused. Removing the need to pass in kernel parameters through
+	  command line. For example, iommu.strict=0 on ARM64. If this is
+	  enabled, you can still disable with kernel parameters, such as
+	  iommu.strict=1 depending on the architecture.
+
+	  If unsure, say N here.
+
 config OF_IOMMU
        def_bool y
        depends on OF && IOMMU_API
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 33a982e33716369..5acb98e79b5b32d 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -43,7 +43,12 @@
 #else
 static unsigned int iommu_def_domain_type = IOMMU_DOMAIN_DMA;
 #endif
+
+#ifdef CONFIG_IOMMU_DMA_DEFAULT_LAZY_MODE
+static bool iommu_dma_strict __read_mostly;
+#else
 static bool iommu_dma_strict __read_mostly = true;
+#endif

 struct iommu_callback_data {
 	const struct iommu_ops *ops;
--
1.8.3