dt-bindings: riscv: add SBI PMU event mappings

The SBI PMU extension requires a firmware to be aware of the event to
counter/mhpmevent mappings supported by the hardware. OpenSBI may use
DeviceTree to describe the PMU mappings. This binding is currently
described in markdown in OpenSBI (since v1.0 in Dec 2021) & used by QEMU
since v7.2.0.

Import the binding for use while validating dtb dumps from QEMU and
upcoming hardware (eg JH7110 SoC) that will make use of the event
mapping.

Link: https://github.com/riscv-software-src/opensbi/blob/master/docs/pmu_support.md
Link: https://github.com/riscv-non-isa/riscv-sbi-doc/blob/master/riscv-sbi.adoc # Performance Monitoring Unit Extension
Co-developed-by: Atish Patra <atishp@rivosinc.com>
Signed-off-by: Atish Patra <atishp@rivosinc.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230113205435.122712-1-conor@kernel.orgSigned-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/perf/riscv,pmu.yaml

+# SPDX-License-Identifier: BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/perf/riscv,pmu.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: RISC-V SBI PMU events
+
+maintainers:
+  - Atish Patra <atishp@rivosinc.com>
+
+description: |
+  The SBI PMU extension allows supervisor software to configure, start and
+  stop any performance counter at anytime. Thus, a user can leverage all
+  capabilities of performance analysis tools, such as perf, if the SBI PMU
+  extension is enabled. The following constraints apply:
+
+    The platform must provide information about PMU event to counter mappings
+    either via device tree or another way, specific to the platform.
+    Without the event to counter mappings, the SBI PMU extension cannot be used.
+
+    Platforms should provide information about the PMU event selector values
+    that should be encoded in the expected value of MHPMEVENTx while configuring
+    MHPMCOUNTERx for that specific event. The can either be done via device tree
+    or another way, specific to the platform.
+    The exact value to be written to MHPMEVENTx is completely dependent on the
+    platform.
+
+    For information on the SBI specification see the section "Performance
+    Monitoring Unit Extension" of:
+      https://github.com/riscv-non-isa/riscv-sbi-doc/blob/master/riscv-sbi.adoc
+
+properties:
+  compatible:
+    const: riscv,pmu
+
+  riscv,event-to-mhpmevent:
+    $ref: /schemas/types.yaml#/definitions/uint32-matrix
+    description:
+      Represents an ONE-to-ONE mapping between a PMU event and the event
+      selector value that the platform expects to be written to the MHPMEVENTx
+      CSR for that event.
+      The mapping is encoded in an matrix format where each element represents
+      an event.
+      This property shouldn't encode any raw hardware event.
+    items:
+      items:
+        - description: event_idx, a 20-bit wide encoding of the event type and
+            code. Refer to the SBI specification for a complete description of
+            the event types and codes.
+        - description: upper 32 bits of the event selector value for MHPMEVENTx
+        - description: lower 32 bits of the event selector value for MHPMEVENTx
+
+  riscv,event-to-mhpmcounters:
+    $ref: /schemas/types.yaml#/definitions/uint32-matrix
+    description:
+      Represents a MANY-to-MANY mapping between a range of events and all the
+      MHPMCOUNTERx in a bitmap format that can be used to monitor these range
+      of events. The information is encoded in an matrix format where each
+      element represents a certain range of events and corresponding counters.
+      This property shouldn't encode any raw event.
+    items:
+      items:
+        - description: first event_idx of the range of events
+        - description: last event_idx of the range of events
+        - description: bitmap of MHPMCOUNTERx for this event
+
+  riscv,raw-event-to-mhpmcounters:
+    $ref: /schemas/types.yaml#/definitions/uint32-matrix
+    description:
+      Represents an ONE-to-MANY or MANY-to-MANY mapping between the rawevent(s)
+      and all the MHPMCOUNTERx in a bitmap format that can be used to monitor
+      that raw event.
+      The encoding of the raw events are platform specific. The information is
+      encoded in a matrix format where each element represents the specific raw
+      event(s).
+      If a platform directly encodes each raw PMU event as a unique ID, the
+      value of variant must be 0xffffffff_ffffffff.
+    items:
+      items:
+        - description:
+            upper 32 invariant bits for the range of events
+        - description:
+            lower 32 invariant bits for the range of events
+        - description:
+            upper 32 bits of the variant bit mask for the range of events
+        - description:
+            lower 32 bits of the variant bit mask for the range of events
+        - description:
+            bitmap of all MHPMCOUNTERx that can monitor the range of events
+
+dependencies:
+  "riscv,event-to-mhpmevent": [ "riscv,event-to-mhpmcounters" ]
+  "riscv,event-to-mhpmcounters": [ "riscv,event-to-mhpmevent" ]
+
+required:
+  - compatible
+
+additionalProperties: false
+
+examples:
+  - |
+    pmu {
+        compatible = "riscv,pmu";
+        riscv,event-to-mhpmevent = <0x0000B 0x0000 0x0001>;
+        riscv,event-to-mhpmcounters = <0x00001 0x00001 0x00000001>,
+                                      <0x00002 0x00002 0x00000004>,
+                                      <0x00003 0x0000A 0x00000ff8>,
+                                      <0x10000 0x10033 0x000ff000>;
+        riscv,raw-event-to-mhpmcounters =
+            /* For event ID 0x0002 */
+            <0x0000 0x0002 0xffffffff 0xffffffff 0x00000f8>,
+            /* For event ID 0-4 */
+            <0x0 0x0 0xffffffff 0xfffffff0 0x00000ff0>,
+            /* For event ID 0xffffffff0000000f - 0xffffffff000000ff */
+            <0xffffffff 0x0 0xffffffff 0xffffff0f 0x00000ff0>;
+    };
+
+  - |
+    /*
+     * For HiFive Unmatched board the encodings can be found here
+     * https://sifive.cdn.prismic.io/sifive/1a82e600-1f93-4f41-b2d8-86ed8b16acba_fu740-c000-manual-v1p6.pdf
+     *
+     * This example also binds standard SBI PMU hardware IDs to U74 PMU event
+     * codes, U74 uses a bitfield for events encoding, so several U74 events
+     * can be bound to a single perf ID.
+     * See SBI PMU hardware IDs in arch/riscv/include/asm/sbi.h
+     */
+    pmu {
+          compatible = "riscv,pmu";
+          riscv,event-to-mhpmevent =
+              /* SBI_PMU_HW_CACHE_REFERENCES -> Instruction or Data cache/ITIM busy */
+              <0x00003 0x00000000 0x1801>,
+              /* SBI_PMU_HW_CACHE_MISSES -> Instruction or Data cache miss or MMIO access */
+              <0x00004 0x00000000 0x0302>,
+              /* SBI_PMU_HW_BRANCH_INSTRUCTIONS -> Conditional branch retired */
+              <0x00005 0x00000000 0x4000>,
+              /* SBI_PMU_HW_BRANCH_MISSES -> Branch or jump misprediction */
+              <0x00006 0x00000000 0x6001>,
+              /* L1D_READ_MISS -> Data cache miss or MMIO access */
+              <0x10001 0x00000000 0x0202>,
+              /* L1D_WRITE_ACCESS -> Data cache write-back */
+              <0x10002 0x00000000 0x0402>,
+              /* L1I_READ_ACCESS -> Instruction cache miss */
+              <0x10009 0x00000000 0x0102>,
+              /* LL_READ_MISS -> UTLB miss */
+              <0x10011 0x00000000 0x2002>,
+              /* DTLB_READ_MISS -> Data TLB miss */
+              <0x10019 0x00000000 0x1002>,
+              /* ITLB_READ_MISS-> Instruction TLB miss */
+              <0x10021 0x00000000 0x0802>;
+          riscv,event-to-mhpmcounters = <0x00003 0x00006 0x18>,
+                                        <0x10001 0x10002 0x18>,
+                                        <0x10009 0x10009 0x18>,
+                                        <0x10011 0x10011 0x18>,
+                                        <0x10019 0x10019 0x18>,
+                                        <0x10021 0x10021 0x18>;
+          riscv,raw-event-to-mhpmcounters = <0x0 0x0 0xffffffff 0xfc0000ff 0x18>,
+                                            <0x0 0x1 0xffffffff 0xfff800ff 0x18>,
+                                            <0x0 0x2 0xffffffff 0xffffe0ff 0x18>;
+    };