pub trait Cppc {
// Required methods
fn probe(&self, reg_id: u32) -> SbiRet;
fn read(&self, reg_id: u32) -> SbiRet;
fn read_hi(&self, reg_id: u32) -> SbiRet;
fn write(&self, reg_id: u32, val: u64) -> SbiRet;
}Expand description
SBI CPPC support extension.
ACPI defines the Collaborative Processor Performance Control (CPPC) mechanism, which is an abstract and flexible mechanism for the supervisor-mode power-management software, to collaborate with an entity in the platform to manage the performance of the processors.
The SBI CPPC extension provides an abstraction to access the CPPC registers through SBI calls. The CPPC registers can be memory locations shared with a separate platform entity such as a BMC. Even though CPPC is defined in the ACPI specification, it may be possible to implement a CPPC driver based on a Device Tree.
The table below defines 32-bit identifiers for all CPPC registers to be used by the SBI CPPC functions. The first half of the 32-bit register space corresponds to the registers as defined by the ACPI specification. The second half provides the information not defined in the ACPI specification, but is additionally required by the supervisor-mode power-management software.
| Register ID | Register | Bit Width | Attribute | Description |
|---|---|---|---|---|
| 0x00000000 | HighestPerformance | 32 | Read-only | ACPI Spec 6.5: 8.4.6.1.1.1 |
| 0x00000001 | NominalPerformance | 32 | Read-only | ACPI Spec 6.5: 8.4.6.1.1.2 |
| 0x00000002 | LowestNonlinearPerformance | 32 | Read-only | ACPI Spec 6.5: 8.4.6.1.1.4 |
| 0x00000003 | LowestPerformance | 32 | Read-only | ACPI Spec 6.5: 8.4.6.1.1.5 |
| 0x00000004 | GuaranteedPerformanceRegister | 32 | Read-only | ACPI Spec 6.5: 8.4.6.1.1.6 |
| 0x00000005 | DesiredPerformanceRegister | 32 | Read / Write | ACPI Spec 6.5: 8.4.6.1.2.3 |
| 0x00000006 | MinimumPerformanceRegister | 32 | Read / Write | ACPI Spec 6.5: 8.4.6.1.2.2 |
| 0x00000007 | MaximumPerformanceRegister | 32 | Read / Write | ACPI Spec 6.5: 8.4.6.1.2.1 |
| 0x00000008 | PerformanceReductionToleranceRegister | 32 | Read / Write | ACPI Spec 6.5: 8.4.6.1.2.4 |
| 0x00000009 | TimeWindowRegister | 32 | Read / Write | ACPI Spec 6.5: 8.4.6.1.2.5 |
| 0x0000000A | CounterWraparoundTime | 32 / 64 | Read-only | ACPI Spec 6.5: 8.4.6.1.3.1 |
| 0x0000000B | ReferencePerformanceCounterRegister | 32 / 64 | Read-only | ACPI Spec 6.5: 8.4.6.1.3.1 |
| 0x0000000C | DeliveredPerformanceCounterRegister | 32 / 64 | Read-only | ACPI Spec 6.5: 8.4.6.1.3.1 |
| 0x0000000D | PerformanceLimitedRegister | 32 | Read / Write | ACPI Spec 6.5: 8.4.6.1.3.2 |
| 0x0000000E | CPPCEnableRegister | 32 | Read / Write | ACPI Spec 6.5: 8.4.6.1.4 |
| 0x0000000F | AutonomousSelectionEnable | 32 | Read / Write | ACPI Spec 6.5: 8.4.6.1.5 |
| 0x00000010 | AutonomousActivityWindowRegister | 32 | Read / Write | ACPI Spec 6.5: 8.4.6.1.6 |
| 0x00000011 | EnergyPerformancePreferenceRegister | 32 | Read / Write | ACPI Spec 6.5: 8.4.6.1.7 |
| 0x00000012 | ReferencePerformance | 32 | Read-only | ACPI Spec 6.5: 8.4.6.1.1.3 |
| 0x00000013 | LowestFrequency | 32 | Read-only | ACPI Spec 6.5: 8.4.6.1.1.7 |
| 0x00000014 | NominalFrequency | 32 | Read-only | ACPI Spec 6.5: 8.4.6.1.1.7 |
| 0x00000015 - 0x7FFFFFFF | Reserved for future use. | |||
| 0x80000000 | TransitionLatency | 32 | Read-only | Provides the maximum (worst-case) performance state transition latency in nanoseconds. |
| 0x80000001 - 0xFFFFFFFF | Reserved for future use. |
Required Methods§
Sourcefn probe(&self, reg_id: u32) -> SbiRet
fn probe(&self, reg_id: u32) -> SbiRet
Probe whether the CPPC register as specified by the reg_id parameter
is implemented or not by the platform.
§Return value
If the register is implemented, SbiRet.value will contain the register
width. If the register is not implemented, SbiRet.value will be set to 0.
The possible return error codes returned in SbiRet.error are shown in the table below:
| Error code | Description |
|---|---|
SbiRet::success() | Probe completed successfully. |
SbiRet::invalid_param() | reg_id is reserved. |
SbiRet::failed() | The probe request failed for unspecified or unknown other reasons. |
Sourcefn read(&self, reg_id: u32) -> SbiRet
fn read(&self, reg_id: u32) -> SbiRet
Reads the register as specified in the reg_id parameter.
§Return value
Returns the value of the register in SbiRet.value. When supervisor mode XLEN is 32,
the SbiRet.value will only contain the lower 32 bits of the CPPC register value.
The possible return error codes returned in SbiRet.error are shown in the table below:
| Error code | Description |
|---|---|
SbiRet::success() | Read completed successfully. |
SbiRet::invalid_param() | reg_id is reserved. |
SbiRet::not_supported() | reg_id is not implemented by the platform. |
SbiRet::denied() | reg_id is a write-only register. |
SbiRet::failed() | The read request failed for unspecified or unknown other reasons. |
Sourcefn read_hi(&self, reg_id: u32) -> SbiRet
fn read_hi(&self, reg_id: u32) -> SbiRet
Reads the upper 32-bit value of the register specified in the reg_id
parameter.
§Return value
Returns the value of the register in SbiRet.value. This function always
returns zero in SbiRet.value when supervisor mode XLEN is 64 or higher.
The possible return error codes returned in SbiRet.error are shown in the table below:
| Error code | Description |
|---|---|
SbiRet::success() | Read completed successfully. |
SbiRet::invalid_param() | reg_id is reserved. |
SbiRet::not_supported() | reg_id is not implemented by the platform. |
SbiRet::denied() | reg_id is a write-only register. |
SbiRet::failed() | The read request failed for unspecified or unknown other reasons. |
Sourcefn write(&self, reg_id: u32, val: u64) -> SbiRet
fn write(&self, reg_id: u32, val: u64) -> SbiRet
Writes the value passed in the val parameter to the register as
specified in the reg_id parameter.
§Return value
The possible return error codes returned in SbiRet.error are shown in the table below:
| Error code | Description |
|---|---|
SbiRet::success() | Write completed successfully. |
SbiRet::invalid_param() | reg_id is reserved. |
SbiRet::not_supported() | reg_id is not implemented by the platform. |
SbiRet::denied() | reg_id is a read-only register. |
SbiRet::failed() | The write-request failed for unspecified or unknown other reasons. |