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ACPI v6.5 spec. introduced ClockInput resource descriptor to describe clocks required for devices.
ClockInput (FrequencyNumerator, FrequencyDivisor, Scale, FixedMode, ResourceSource, ˓ResourceSourceIndex)
Examples from ACPI spec.
Case 1: Simple clock input descriptor, with a fixed frequency of 33 1/3 MHz and no Device shown as a clock source.
ClockInput (100, 3, MHz, Fixed,,)
Case 2: Clock input descriptor referencing a variable clock input of 19.2 kHz, with a source device and index.
ClockInput (19200, 1, Hz, Variable, “\\_SB.PCI0.CLK4”, 3)
SCMI Clock Driver with ClockInput resources
Device (SCMI) {
Name (_HID, "PNP####")
...
}
Device(I2C) {
...
Name(_CLK, 13) // SCMI clock ID for I2C root clock
Method (_CRS, 0, NotSerialized)
{
Name (RBUF, ResourceTemplate () {
MEMORY32FIXED(ReadWrite, 0x30A40000, 0x14, )
Interrupt(ResourceConsumer, Level, ActiveHigh, Exclusive) { 69 }
ClockInput (24, 1, MHz, Variable, “\\_SB.SCMI”, _CLK)
})
Return(RBUF)
}
...
}