[PATCH 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
defalut, 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..5ec9780f564eaf8 100644
--- a/drivers/iommu/Kconfig
+++ b/drivers/iommu/Kconfig
@@ -85,6 +85,20 @@ config IOMMU_DEFAULT_PASSTHROUGH

 	  If unsure, say N here.

+config IOMMU_LAZY_MODE
+	bool "IOMMU use lazy mode to flush IOTLB and free IOVA"
+	depends on IOMMU_API
+	help
+	  For every IOMMU 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 iommu.strict=0
+	  through command line on ARM64(Now, intel_iommu, amd_iommu, s390_iommu use
+	  lazy mode as deault). If this is enabled, you can still disable with kernel
+	  parameters, such as iommu.strict=1, intel_iommu=strict, amd_iommu=fullflush
+	  or s390_iommu=strict 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..e307d70d1578b3b 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_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