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

Zhen Lei
2019-05-30T03:48:25Z

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@huawei.com>
---
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