80 lines
3.7 KiB
Markdown
80 lines
3.7 KiB
Markdown
OpenSBI SBI PMU extension support
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==================================
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SBI PMU extension supports allow supervisor software to configure/start/stop
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any performance counter at anytime. Thus, an user can leverage full
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capability of performance analysis tools such as perf if SBI PMU extension is
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enabled. The OpenSBI implementation makes the following assumptions about the
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hardware platform.
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* MCOUNTINHIBIT CSR must be implemented in the hardware. Otherwise, SBI PMU
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extension will not be enabled.
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* The platform must provide information about PMU event to counter mapping
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via device tree or platform specific hooks. Otherwise, SBI PMU extension will
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not be enabled.
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* The platforms should provide information about the PMU event selector values
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that should be encoded in the expected value of MHPMEVENTx while configuring
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MHPMCOUNTERx for that specific event. This can be done via a device tree or
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platform specific hooks. The exact value to be written to he MHPMEVENTx is
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completely depends on platform. Generic platform writes the zero-extended event_idx
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as the expected value for hardware cache/generic events as suggested by the SBI
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specification.
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SBI PMU Device Tree Bindings
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----------------------------
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Platforms may choose to describe PMU event selector and event to counter mapping
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values via device tree. The following sections describes the PMU DT node
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bindings in details.
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* **compatible** (Mandatory) - The compatible string of SBI PMU device tree node.
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This DT property must have the value **riscv,pmu**.
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* **pmu,event-to-mhpmevent**(Optional) - It represents an ONE-to-ONE mapping
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between a PMU event and the event selector value that platform expects to be
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written to the MHPMEVENTx CSR for that event. The mapping is encoded in a
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table format where each row represents an event. The first column represent the
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event idx where the 2nd & 3rd column represent the event selector value that
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should be encoded in the expected value to be written in MHPMEVENTx.
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This property shouldn't encode any raw hardware event.
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* **pmu,event-to-mhpmcounters**(Optional) - It represents a MANY-to-MANY
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mapping between a range of events and all the MHPMCOUNTERx in a bitmap format
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that can be used to monitor these range of events. The information is encoded in
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a table format where each row represent a certain range of events and
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corresponding counters. The first column represents starting of the pmu event id
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and 2nd column represents the end of the pmu event id. The third column
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represent a bitmap of all the MHPMCOUNTERx. This property is mandatory if
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event-to-mhpmevent is present. Otherwise, it can be omitted. This property
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shouldn't encode any raw event.
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* **pmu,raw-event-to-mhpmcounters**(Optional) - It represents an ONE-to-MANY
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mapping between a raw event and all the MHPMCOUNTERx in a bitmap format that can
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be used to monitor that raw event. The information is encoded in a table format
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where each raw represent a specific raw event. The first column stores the
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expected event selector value that should be encoded in the expected value to be
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written in MHPMEVENTx. The second column stores a bitmap of all the MHPMCOUNTERx
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that can be used for monitoring the specified event.
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*Note:* A platform may choose to provide the mapping between event & counters
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via platform hooks rather than the device tree.
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### Example
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```
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pmu {
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compatible = "riscv,pmu";
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interrupts = <0x100>;
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interrupt-parent = <&plic>
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pmu,event-to-mhpmevent = <0x0000B 0x0000 0x0001>,
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pmu,event-to-mhpmcounters = <0x00001 0x00001 0x00000001>,
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<0x00002 0x00002 0x00000004>,
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<0x00003 0x0000A 0x00000ff8>,
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<0x10000 0x10033 0x000ff000>,
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pmu,raw-event-to-mhpmcounters = <0x0000 0x0002 0x00000f8>,
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<0x0000 0x0003 0x00000ff0>,
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};
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```
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