dt-bindings: riscv: add SBI PMU event mappings

From: Conor Dooley <[email protected]>

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 <[email protected]>

Signed-off-by Atish Patra <[email protected]>

Signed-off-by Conor Dooley <[email protected]>

---
Changes in v2:
- use the schema mechanism for dependancies between properties
- +CC perf maintainers...
- move the matrix element descriptions into regular item descriptions rather than doing so freeform in the property description
- drop some description text that no longer applies since changes were made to the SBI spec
- drop mention of the "generic platform" which is OpenSBI specific
- drop the min/max items from the matrices, they don't appear to be needed?

---
 .../devicetree/bindings/perf/riscv,pmu.yaml   | 154 ++++++++++++++++++
 1 file changed, 154 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/perf/riscv,pmu.yaml

Documentation/devicetree/bindings/perf/riscv,pmu.yaml new file +36 -0

new file mode 100644
index 000000000000..b50b69ed4599
@@ -0,0 +1,154 @@
+# 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 <[email protected]>
+
+description: |
+  SBI PMU extension supports allow supervisor software to configure, start &
+  stop any performance counter at anytime. Thus, a user can leverage full
+  capability of performance analysis tools such as perf if the SBI PMU
+  extension is enabled. The OpenSBI implementation makes the following
+  assumptions about the hardware platform:
+
+    The platform must provide information about PMU event to counter mapping
+    via device tree or platform specific hooks. Otherwise, the SBI PMU
+    extension will not be enabled.
+
+    The 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. This can be done via a
+    device tree or platform specific hooks. The exact value to be written to
+    the MHPMEVENTx is completely dependent on the platform.
+
+    For information on the SBI spec see:
+      https://github.com/riscv-non-isa/riscv-sbi-doc/blob/master/riscv-sbi.adoc
+
+properties:
+  compatible:
+    const: riscv,pmu
+
+  riscv,event-to-mhpmevent:

Documentation/devicetree/bindings/perf/riscv,pmu.yaml new file +94 -0

+      - 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:
+      - 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 id's to U74 PMU event
+     * codes, U74 uses a bitfield for events encoding, so several U74 events
+     * can be bound to single perf id.
+     * See SBI PMU hardware id's in OpenSBI's include/sbi/sbi_ecall_interface.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>;
+    };

Hi Conor,

Quoted 30 lines · Conor Dooley

From: Conor Dooley <[email protected]>

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 <[email protected]>

Signed-off-by Atish Patra <[email protected]>

Signed-off-by Conor Dooley <[email protected]>

---
Changes in v2:
- use the schema mechanism for dependancies between properties
- +CC perf maintainers...
- move the matrix element descriptions into regular item descriptions rather than doing so freeform in the property description
- drop some description text that no longer applies since changes were made to the SBI spec
- drop mention of the "generic platform" which is OpenSBI specific
- drop the min/max items from the matrices, they don't appear to be needed?

Documentation/devicetree/bindings/perf/riscv,pmu.yaml new file +1 -0

+  riscv,event-to-mhpmevent:

Documentation/devicetree/bindings/perf/riscv,pmu.yaml line 46

Quoted 10 lines

Documentation/devicetree/bindings/perf/riscv,pmu.yaml new file +10 -0

+    $ref: /schemas/types.yaml#/definitions/uint32-matrix
+    description:
+      Represents an ONE-to-ONE mapping between a PMU event and the event
+      selector value that 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:
+      - description: event idx

It might be good to clarify that this refers specifically to "event_idx" from the SBI specification.

Documentation/devicetree/bindings/perf/riscv,pmu.yaml line 48

Quoted 2 lines

Documentation/devicetree/bindings/perf/riscv,pmu.yaml new file +2 -0

+      - description: upper 32 bits of the event selector value for MHPMEVENTx
+      - description: lower 32 bits of the event selector value for MHPMEVENTx

Since you are describing the the columns of the matrix here, I believe these entries need to go under two levels of "items:". The same applies for the other properties.

Documentation/devicetree/bindings/perf/riscv,pmu.yaml line 60

Quoted 12 lines

Documentation/devicetree/bindings/perf/riscv,pmu.yaml new file +12 -0

+
+  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:
+      - description: upper 32 bits of the pmu event id
+      - description: lower 32 bits of the pmu event id

These two cells represent the start and end of a range of 32-bit values (again the "event_idx" from the SBI specification), not 32-bit components of a 64-bit value.