[PATCH v8 1/7] iommu: enhance IOMMU default DMA mode build options

[Zhen Lei]

First, add build option IOMMU_DEFAULT_{LAZY|STRICT}, so that we have the
opportunity to set {lazy|strict} mode as default at build time. Then put
the three config options in an choice, make people can only choose one of
the three at a time.

Signed-off-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx>
---
 drivers/iommu/Kconfig | 42 +++++++++++++++++++++++++++++++++++-------
 drivers/iommu/iommu.c |  3 ++-
 2 files changed, 37 insertions(+), 8 deletions(-)

diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
index 83664db5221df02..d6a1a45f80ffbf5 100644
--- a/drivers/iommu/Kconfig
+++ b/drivers/iommu/Kconfig
@@ -75,17 +75,45 @@ config IOMMU_DEBUGFS
 	  debug/iommu directory, and then populate a subdirectory with
 	  entries as required.
 
-config IOMMU_DEFAULT_PASSTHROUGH
-	bool "IOMMU passthrough by default"
+choice
+	prompt "IOMMU default DMA mode"
 	depends on IOMMU_API
-        help
-	  Enable passthrough by default, removing the need to pass in
-	  iommu.passthrough=on or iommu=pt through command line. If this
-	  is enabled, you can still disable with iommu.passthrough=off
-	  or iommu=nopt depending on the architecture.
+	default IOMMU_DEFAULT_STRICT
+	help
+	  This option allows IOMMU DMA mode to be chose at build time, to
+	  override the default DMA mode of each ARCHs, removing the need to
+	  pass in kernel parameters through command line. You can still use
+	  ARCHs specific boot options to override this option again.
+
+config IOMMU_DEFAULT_PASSTHROUGH
+	bool "passthrough"
+	help
+	  In this mode, the DMA access through IOMMU without any addresses
+	  translation. That means, the wrong or illegal DMA access can not
+	  be caught, no error information will be reported.
 
 	  If unsure, say N here.
 
+config IOMMU_DEFAULT_LAZY
+	bool "lazy"
+	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.
+
+config IOMMU_DEFAULT_STRICT
+	bool "strict"
+	help
+	  For every IOMMU DMA unmap operation, the flush operation of IOTLB and
+	  the free operation of IOVA are guaranteed to be done in the unmap
+	  function.
+
+	  This mode is safer than the two above, but it maybe slower in some
+	  high performace scenarios.
+
+endchoice
+
 config OF_IOMMU
        def_bool y
        depends on OF && IOMMU_API
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 67ee6623f9b2a4d..56bce221285b15f 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -43,7 +43,8 @@
 #else
 static unsigned int iommu_def_domain_type = IOMMU_DOMAIN_DMA;
 #endif
-static bool iommu_dma_strict __read_mostly = true;
+static bool iommu_dma_strict __read_mostly =
+			IS_ENABLED(CONFIG_IOMMU_DEFAULT_STRICT);
 
 struct iommu_group {
 	struct kobject kobj;
-- 
1.8.3