[PATCH] iommu: Add Kconfig help text for IOMMU_SVA

[Jacob Pan]

Shared Virtual Addressing (SVA) is not immediately intuitive to people
who work outside IOMMU subsystem, add some explanation to make it less
opaque.
Link: https://lore.kernel.org/lkml/ZE70doFi8X3KgfrV@xxxxxxxx/t/#meaa938c91857665b376db59e16b532ba9d4ea013
Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
---
 drivers/iommu/Kconfig | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
index db98c3f86e8c..0f7181007dc1 100644
--- a/drivers/iommu/Kconfig
+++ b/drivers/iommu/Kconfig
@@ -1,4 +1,4 @@
-# SPDX-License-Identifier: GPL-2.0-only
+# PDX-License-Identifier: GPL-2.0-only
 # The IOVA library may also be used by non-IOMMU_API users
 config IOMMU_IOVA
 	tristate
@@ -155,7 +155,14 @@ config IOMMU_DMA
 
 # Shared Virtual Addressing
 config IOMMU_SVA
-	bool
+	bool "Shared Virtual Addressing"
+	help
+	  IOMMU and CPU share page tables for user processes thus DMA can use
+	  CPU virtual address. Under intel architecture, it is also called
+	  Shared Virtual Memory (SVM).
+	  With SVA, DMA requests are tagged with PCIe Process Address Space ID
+	  (PASID) or Substream ID (ARM SMMU term) with which page tables are
+	  associated.
 
 config FSL_PAMU
 	bool "Freescale IOMMU support"
-- 
2.25.1