[PATCH v2 7/8] docs: update the description about RISC-V AIA

[Yong-Xuan Wang <yongxuan.wang@sifive.com>]

Add the description about "-accel kvm,kernel-irqchip=off" into
docs/specs/riscv-aia.rst and docs/system/riscv/virt.rst.

Signed-off-by: Yong-Xuan Wang <yongxuan.wang@sifive.com>
---
 docs/specs/riscv-aia.rst   | 24 ++++++++++++++++++------
 docs/system/riscv/virt.rst | 10 ++++++----
 2 files changed, 24 insertions(+), 10 deletions(-)

diff --git a/docs/specs/riscv-aia.rst b/docs/specs/riscv-aia.rst
index 8097e2f89744..38797cca4998 100644
--- a/docs/specs/riscv-aia.rst
+++ b/docs/specs/riscv-aia.rst
@@ -25,11 +25,16 @@ When running KVM:
 - no m-mode is provided, so there is no m-mode APLIC or IMSIC emulation regardless of
   the AIA mode chosen
 - with "aia=aplic", s-mode APLIC will be emulated by userspace
-- with "aia=aplic-imsic" there are two possibilities.  If no additional KVM option
-  is provided there will be no APLIC or IMSIC emulation in userspace, and the virtual
-  machine will use the provided in-kernel APLIC and IMSIC controllers.  If the user
-  chooses to use the irqchip in split mode via "-accel kvm,kernel-irqchip=split",
-  s-mode APLIC will be emulated while using the s-mode IMSIC from the irqchip
+- with "aia=aplic-imsic" there are three possibilities.
+    - If no additional KVM option is provided there will be no APLIC or IMSIC emulation
+      in userspace, and the virtual machine will use the provided in-kernel APLIC and
+      IMSIC controllers.
+    - If the user chooses to use the irqchip in split mode via
+      "-accel kvm,kernel-irqchip=split", s-mode APLIC will be emulated while using
+      the s-mode IMSIC from the irqchip.
+    - If the user disables the in-kernel irqchip via "-accel kvm,kernel-irqchip=off",
+      both s-mode APLIC and IMSIC controller will be emulated.
+
 
 The following table summarizes how the AIA and accelerator options defines what
 we will emulate in userspace:
@@ -75,9 +80,16 @@ we will emulate in userspace:
      - in-kernel
      - in-kernel
    * - kvm
-     - irqchip=split
+     - kernel-irqchip=split
      - aplic-imsic
      - n/a
      - n/a
      - emul
      - in-kernel
+   * - kvm
+     - kernel-irqchip=off
+     - aplic-imsic
+     - n/a
+     - n/a
+     - emul
+     - emul
diff --git a/docs/system/riscv/virt.rst b/docs/system/riscv/virt.rst
index 60850970ce83..96d7ee1ebc64 100644
--- a/docs/system/riscv/virt.rst
+++ b/docs/system/riscv/virt.rst
@@ -129,12 +129,14 @@ The following machine-specific options are supported:
   MSIs. When not specified, this option is assumed to be "none" which selects
   SiFive PLIC to handle wired interrupts.
 
-  This option also interacts with '-accel kvm'.  When using "aia=aplic-imsic"
-  with KVM, it is possible to set the use of the kernel irqchip in split mode
+  This option also interacts with '-accel kvm', when using "aia=aplic-imsic"
+  with KVM.  It is possible to set the use of the kernel irqchip in split mode
   by using "-accel kvm,kernel-irqchip=split".  In this case the ``virt`` machine
   will emulate the APLIC controller instead of using the APLIC controller from
-  the irqchip.  See :ref:`riscv-aia` for more details on all available AIA
-  modes.
+  the in-kernel irqchip. Or the kernel irqchip can be disabled by using
+  "-accel kvm,kernel-irqchip=off". In this case the ``virt`` machine will
+  emulate the APLIC and IMSIC controller in user-space instead of using in-kernel
+  irqchip.  See :ref:`riscv-aia` for more details on all available AIA modes.
 
 - aia-guests=nnn
 
-- 
2.17.1