[PATCH v5 1/2] dt-bindings: cpufreq: add virtual cpufreq device

[David Dai <davidai@google.com>]

Adding bindings to represent a virtual cpufreq device.

Virtual machines may expose MMIO regions for a virtual cpufreq device
for guests to read frequency information or to request frequency
selection. The virtual cpufreq device has an individual controller for
each frequency domain. Performance points for a given domain can be
normalized across all domains for ease of allowing for virtual machines
to migrate between hosts.

Co-developed-by: Saravana Kannan <saravanak@google.com>
Signed-off-by: Saravana Kannan <saravanak@google.com>
Signed-off-by: David Dai <davidai@google.com>
---
 .../cpufreq/qemu,cpufreq-virtual.yaml         | 110 ++++++++++++++++++
 1 file changed, 110 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/cpufreq/qemu,cpufreq-virtual.yaml

diff --git a/Documentation/devicetree/bindings/cpufreq/qemu,cpufreq-virtual.yaml b/Documentation/devicetree/bindings/cpufreq/qemu,cpufreq-virtual.yaml
new file mode 100644
index 000000000000..cd617baf75e7
--- /dev/null
+++ b/Documentation/devicetree/bindings/cpufreq/qemu,cpufreq-virtual.yaml
@@ -0,0 +1,110 @@
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/cpufreq/qemu,cpufreq-virtual.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Virtual CPUFreq
+
+maintainers:
+  - David Dai <davidai@google.com>
+  - Saravana Kannan <saravanak@google.com>
+
+description:
+  Virtual CPUFreq is a virtualized driver in guest kernels that sends frequency
+  selection of its vCPUs as a hint to the host through MMIO regions. Each vCPU
+  is associated with a frequency domain which can be shared with other vCPUs.
+  Each frequency domain has its own set of registers for frequency controls.
+
+properties:
+  compatible:
+    const: qemu,virtual-cpufreq
+
+  reg:
+    maxItems: 1
+    description:
+      Address and size of region containing frequency controls for each of the
+      frequency domains. Regions for each frequency domain is placed
+      contiguously and contain registers for controlling DVFS(Dynamic Frequency
+      and Voltage) characteristics. The size of the region is proportional to
+      total number of frequency domains. This device also needs the CPUs to
+      list their OPPs using operating-points-v2 tables. The OPP tables for the
+      CPUs should use normalized "frequency" values where the OPP with the
+      highest performance among all the vCPUs is listed as 1024 KHz. The rest
+      of the frequencies of all the vCPUs should be normalized based on their
+      performance relative to that 1024 KHz OPP. This makes it much easier to
+      migrate the VM across systems which might have different physical CPU
+      OPPs.
+
+required:
+  - compatible
+  - reg
+
+additionalProperties: false
+
+examples:
+  - |
+    // This example shows a two CPU configuration with a frequency domain
+    // for each CPU showing normalized performance points.
+    cpus {
+      #address-cells = <1>;
+      #size-cells = <0>;
+
+      cpu@0 {
+        compatible = "arm,armv8";
+        device_type = "cpu";
+        reg = <0x0>;
+        operating-points-v2 = <&opp_table0>;
+      };
+
+      cpu@1 {
+        compatible = "arm,armv8";
+        device_type = "cpu";
+        reg = <0x0>;
+        operating-points-v2 = <&opp_table1>;
+      };
+    };
+
+    opp_table0: opp-table-0 {
+      compatible = "operating-points-v2";
+
+      opp64000 { opp-hz = /bits/ 64 <64000>; };
+      opp128000 { opp-hz = /bits/ 64 <128000>; };
+      opp192000 { opp-hz = /bits/ 64 <192000>; };
+      opp256000 { opp-hz = /bits/ 64 <256000>; };
+      opp320000 { opp-hz = /bits/ 64 <320000>; };
+      opp384000 { opp-hz = /bits/ 64 <384000>; };
+      opp425000 { opp-hz = /bits/ 64 <425000>; };
+    };
+
+    opp_table1: opp-table-1 {
+      compatible = "operating-points-v2";
+
+      opp64000 { opp-hz = /bits/ 64 <64000>; };
+      opp128000 { opp-hz = /bits/ 64 <128000>; };
+      opp192000 { opp-hz = /bits/ 64 <192000>; };
+      opp256000 { opp-hz = /bits/ 64 <256000>; };
+      opp320000 { opp-hz = /bits/ 64 <320000>; };
+      opp384000 { opp-hz = /bits/ 64 <384000>; };
+      opp448000 { opp-hz = /bits/ 64 <448000>; };
+      opp512000 { opp-hz = /bits/ 64 <512000>; };
+      opp576000 { opp-hz = /bits/ 64 <576000>; };
+      opp640000 { opp-hz = /bits/ 64 <640000>; };
+      opp704000 { opp-hz = /bits/ 64 <704000>; };
+      opp768000 { opp-hz = /bits/ 64 <768000>; };
+      opp832000 { opp-hz = /bits/ 64 <832000>; };
+      opp896000 { opp-hz = /bits/ 64 <896000>; };
+      opp960000 { opp-hz = /bits/ 64 <960000>; };
+      opp1024000 { opp-hz = /bits/ 64 <1024000>; };
+
+    };
+
+    soc {
+      #address-cells = <1>;
+      #size-cells = <1>;
+
+      cpufreq@1040000 {
+        compatible = "qemu,virtual-cpufreq";
+        reg = <0x1040000 0x10>;
+      };
+    };
-- 
2.43.0.429.g432eaa2c6b-goog