[PATCH V4 2/2] kvm/x86 : add document for coalesced pio

[Peng Hao <peng.hao2@zte.com.cn>]

Signed-off-by: Peng Hao <peng.hao2@zte.com.cn>
---
 Documentation/virtual/kvm/00-INDEX          |  2 ++
 Documentation/virtual/kvm/coalesced-pio.txt | 15 +++++++++++++++
 2 files changed, 17 insertions(+)
 create mode 100644 Documentation/virtual/kvm/coalesced-pio.txt

diff --git a/Documentation/virtual/kvm/00-INDEX b/Documentation/virtual/kvm/00-INDEX
index 3492458..4b7a37b 100644
--- a/Documentation/virtual/kvm/00-INDEX
+++ b/Documentation/virtual/kvm/00-INDEX
@@ -9,6 +9,8 @@ arm
 	- internal ABI between the kernel and HYP (for arm/arm64)
 cpuid.txt
 	- KVM-specific cpuid leaves (x86).
+coalesced-pio.txt
+	- KVM_CAP_COALESCED_PIO
 devices/
 	- KVM_CAP_DEVICE_CTRL userspace API.
 halt-polling.txt
diff --git a/Documentation/virtual/kvm/coalesced-pio.txt b/Documentation/virtual/kvm/coalesced-pio.txt
new file mode 100644
index 0000000..38dac11
--- /dev/null
+++ b/Documentation/virtual/kvm/coalesced-pio.txt
@@ -0,0 +1,15 @@
+Linux KVM Coalesced PIO:
+============================
+Coalesced pio is base on coalesced mmio. When the write access to a port
+of a device does a simple work (just like setting a register ID or address
+index), then we can use coalesced pio.
+
+Setting a port as coalesced pio, the write access to the port don't need to
+exit to userspace, and just record the value in shared coalesced ring in kernel.
+Then following access to another port of the same device which relys on the
+first port's setting or a read access to the first port will set the previous
+write value of the first port firstly in usersapce according to the shared
+coalesced ring.
+
+Coalesced pio can be used for rtc 0x70 port, pci-host config port, virtio-pci
+config port and so on.
-- 
1.8.3.1