This adds Kconfig option INTEL_IOMMU_SCALABLE_MODE_DEFAULT_ON
to make it easier for distributions to enable or disable the
Intel IOMMU scalable mode by default during kernel build.

Signed-off-by: Lu Baolu <baolu...@linux.intel.com>
---
 drivers/iommu/Kconfig       | 9 +++++++++
 drivers/iommu/intel-iommu.c | 7 ++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
index e3842eabcfdd..fbdf3fd291d9 100644
--- a/drivers/iommu/Kconfig
+++ b/drivers/iommu/Kconfig
@@ -242,6 +242,15 @@ config INTEL_IOMMU_FLOPPY_WA
          workaround will setup a 1:1 mapping for the first
          16MiB to make floppy (an ISA device) work.
 
+config INTEL_IOMMU_SCALABLE_MODE_DEFAULT_ON
+       prompt "Enable Intel IOMMU scalable mode by default"
+       depends on INTEL_IOMMU
+       help
+         Selecting this option will enable the scalable mode if
+         hardware presents the capability. If this option is not
+         selected, scalable mode support could also be enabled
+         by passing intel_iommu=sm_on to the kernel.
+
 config IRQ_REMAP
        bool "Support for Interrupt Remapping"
        depends on X86_64 && X86_IO_APIC && PCI_MSI && ACPI
diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index 6db6d969e31c..6051fe790c61 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -355,9 +355,14 @@ static phys_addr_t intel_iommu_iova_to_phys(struct 
iommu_domain *domain,
 int dmar_disabled = 0;
 #else
 int dmar_disabled = 1;
-#endif /*CONFIG_INTEL_IOMMU_DEFAULT_ON*/
+#endif /* CONFIG_INTEL_IOMMU_DEFAULT_ON */
 
+#ifdef INTEL_IOMMU_SCALABLE_MODE_DEFAULT_ON
+int intel_iommu_sm = 1;
+#else
 int intel_iommu_sm;
+#endif /* INTEL_IOMMU_SCALABLE_MODE_DEFAULT_ON */
+
 int intel_iommu_enabled = 0;
 EXPORT_SYMBOL_GPL(intel_iommu_enabled);
 
-- 
2.17.1

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