^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 1) .. SPDX-License-Identifier: GPL-2.0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 2)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 3) =======================================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 4) Legacy Documentation of CPU Performance Scaling Drivers
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 5) =======================================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 6)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 7) Included below are historic documents describing assorted
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 8) :doc:`CPU performance scaling <cpufreq>` drivers. They are reproduced verbatim,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 9) with the original white space formatting and indentation preserved, except for
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 10) the added leading space character in every line of text.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 11)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 12)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 13) AMD PowerNow! Drivers
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 14) =====================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 15)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 16) ::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 17)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 18) PowerNow! and Cool'n'Quiet are AMD names for frequency
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 19) management capabilities in AMD processors. As the hardware
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 20) implementation changes in new generations of the processors,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 21) there is a different cpu-freq driver for each generation.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 22)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 23) Note that the driver's will not load on the "wrong" hardware,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 24) so it is safe to try each driver in turn when in doubt as to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 25) which is the correct driver.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 26)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 27) Note that the functionality to change frequency (and voltage)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 28) is not available in all processors. The drivers will refuse
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 29) to load on processors without this capability. The capability
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 30) is detected with the cpuid instruction.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 31)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 32) The drivers use BIOS supplied tables to obtain frequency and
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 33) voltage information appropriate for a particular platform.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 34) Frequency transitions will be unavailable if the BIOS does
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 35) not supply these tables.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 36)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 37) 6th Generation: powernow-k6
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 38)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 39) 7th Generation: powernow-k7: Athlon, Duron, Geode.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 40)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 41) 8th Generation: powernow-k8: Athlon, Athlon 64, Opteron, Sempron.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 42) Documentation on this functionality in 8th generation processors
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 43) is available in the "BIOS and Kernel Developer's Guide", publication
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 44) 26094, in chapter 9, available for download from www.amd.com.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 45)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 46) BIOS supplied data, for powernow-k7 and for powernow-k8, may be
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 47) from either the PSB table or from ACPI objects. The ACPI support
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 48) is only available if the kernel config sets CONFIG_ACPI_PROCESSOR.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 49) The powernow-k8 driver will attempt to use ACPI if so configured,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 50) and fall back to PST if that fails.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 51) The powernow-k7 driver will try to use the PSB support first, and
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 52) fall back to ACPI if the PSB support fails. A module parameter,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 53) acpi_force, is provided to force ACPI support to be used instead
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 54) of PSB support.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 55)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 56)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 57) ``cpufreq-nforce2``
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 58) ===================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 59)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 60) ::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 61)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 62) The cpufreq-nforce2 driver changes the FSB on nVidia nForce2 platforms.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 63)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 64) This works better than on other platforms, because the FSB of the CPU
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 65) can be controlled independently from the PCI/AGP clock.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 66)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 67) The module has two options:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 68)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 69) fid: multiplier * 10 (for example 8.5 = 85)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 70) min_fsb: minimum FSB
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 71)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 72) If not set, fid is calculated from the current CPU speed and the FSB.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 73) min_fsb defaults to FSB at boot time - 50 MHz.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 74)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 75) IMPORTANT: The available range is limited downwards!
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 76) Also the minimum available FSB can differ, for systems
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 77) booting with 200 MHz, 150 should always work.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 78)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 79)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 80) ``pcc-cpufreq``
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 81) ===============
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 82)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 83) ::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 84)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 85) /*
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 86) * pcc-cpufreq.txt - PCC interface documentation
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 87) *
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 88) * Copyright (C) 2009 Red Hat, Matthew Garrett <mjg@redhat.com>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 89) * Copyright (C) 2009 Hewlett-Packard Development Company, L.P.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 90) * Nagananda Chumbalkar <nagananda.chumbalkar@hp.com>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 91) */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 92)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 93)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 94) Processor Clocking Control Driver
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 95) ---------------------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 96)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 97) Contents:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 98) ---------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 99) 1. Introduction
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 100) 1.1 PCC interface
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 101) 1.1.1 Get Average Frequency
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 102) 1.1.2 Set Desired Frequency
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 103) 1.2 Platforms affected
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 104) 2. Driver and /sys details
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 105) 2.1 scaling_available_frequencies
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 106) 2.2 cpuinfo_transition_latency
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 107) 2.3 cpuinfo_cur_freq
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 108) 2.4 related_cpus
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 109) 3. Caveats
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 110)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 111) 1. Introduction:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 112) ----------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 113) Processor Clocking Control (PCC) is an interface between the platform
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 114) firmware and OSPM. It is a mechanism for coordinating processor
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 115) performance (ie: frequency) between the platform firmware and the OS.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 116)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 117) The PCC driver (pcc-cpufreq) allows OSPM to take advantage of the PCC
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 118) interface.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 119)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 120) OS utilizes the PCC interface to inform platform firmware what frequency the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 121) OS wants for a logical processor. The platform firmware attempts to achieve
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 122) the requested frequency. If the request for the target frequency could not be
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 123) satisfied by platform firmware, then it usually means that power budget
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 124) conditions are in place, and "power capping" is taking place.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 125)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 126) 1.1 PCC interface:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 127) ------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 128) The complete PCC specification is available here:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 129) https://acpica.org/sites/acpica/files/Processor-Clocking-Control-v1p0.pdf
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 130)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 131) PCC relies on a shared memory region that provides a channel for communication
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 132) between the OS and platform firmware. PCC also implements a "doorbell" that
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 133) is used by the OS to inform the platform firmware that a command has been
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 134) sent.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 135)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 136) The ACPI PCCH() method is used to discover the location of the PCC shared
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 137) memory region. The shared memory region header contains the "command" and
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 138) "status" interface. PCCH() also contains details on how to access the platform
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 139) doorbell.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 140)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 141) The following commands are supported by the PCC interface:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 142) * Get Average Frequency
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 143) * Set Desired Frequency
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 144)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 145) The ACPI PCCP() method is implemented for each logical processor and is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 146) used to discover the offsets for the input and output buffers in the shared
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 147) memory region.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 148)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 149) When PCC mode is enabled, the platform will not expose processor performance
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 150) or throttle states (_PSS, _TSS and related ACPI objects) to OSPM. Therefore,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 151) the native P-state driver (such as acpi-cpufreq for Intel, powernow-k8 for
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 152) AMD) will not load.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 153)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 154) However, OSPM remains in control of policy. The governor (eg: "ondemand")
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 155) computes the required performance for each processor based on server workload.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 156) The PCC driver fills in the command interface, and the input buffer and
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 157) communicates the request to the platform firmware. The platform firmware is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 158) responsible for delivering the requested performance.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 159)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 160) Each PCC command is "global" in scope and can affect all the logical CPUs in
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 161) the system. Therefore, PCC is capable of performing "group" updates. With PCC
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 162) the OS is capable of getting/setting the frequency of all the logical CPUs in
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 163) the system with a single call to the BIOS.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 164)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 165) 1.1.1 Get Average Frequency:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 166) ----------------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 167) This command is used by the OSPM to query the running frequency of the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 168) processor since the last time this command was completed. The output buffer
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 169) indicates the average unhalted frequency of the logical processor expressed as
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 170) a percentage of the nominal (ie: maximum) CPU frequency. The output buffer
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 171) also signifies if the CPU frequency is limited by a power budget condition.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 172)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 173) 1.1.2 Set Desired Frequency:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 174) ----------------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 175) This command is used by the OSPM to communicate to the platform firmware the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 176) desired frequency for a logical processor. The output buffer is currently
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 177) ignored by OSPM. The next invocation of "Get Average Frequency" will inform
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 178) OSPM if the desired frequency was achieved or not.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 179)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 180) 1.2 Platforms affected:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 181) -----------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 182) The PCC driver will load on any system where the platform firmware:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 183) * supports the PCC interface, and the associated PCCH() and PCCP() methods
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 184) * assumes responsibility for managing the hardware clocking controls in order
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 185) to deliver the requested processor performance
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 186)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 187) Currently, certain HP ProLiant platforms implement the PCC interface. On those
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 188) platforms PCC is the "default" choice.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 189)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 190) However, it is possible to disable this interface via a BIOS setting. In
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 191) such an instance, as is also the case on platforms where the PCC interface
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 192) is not implemented, the PCC driver will fail to load silently.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 193)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 194) 2. Driver and /sys details:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 195) ---------------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 196) When the driver loads, it merely prints the lowest and the highest CPU
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 197) frequencies supported by the platform firmware.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 198)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 199) The PCC driver loads with a message such as:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 200) pcc-cpufreq: (v1.00.00) driver loaded with frequency limits: 1600 MHz, 2933
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 201) MHz
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 202)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 203) This means that the OPSM can request the CPU to run at any frequency in
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 204) between the limits (1600 MHz, and 2933 MHz) specified in the message.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 205)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 206) Internally, there is no need for the driver to convert the "target" frequency
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 207) to a corresponding P-state.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 208)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 209) The VERSION number for the driver will be of the format v.xy.ab.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 210) eg: 1.00.02
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 211) ----- --
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 212) | |
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 213) | -- this will increase with bug fixes/enhancements to the driver
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 214) |-- this is the version of the PCC specification the driver adheres to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 215)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 216)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 217) The following is a brief discussion on some of the fields exported via the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 218) /sys filesystem and how their values are affected by the PCC driver:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 219)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 220) 2.1 scaling_available_frequencies:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 221) ----------------------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 222) scaling_available_frequencies is not created in /sys. No intermediate
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 223) frequencies need to be listed because the BIOS will try to achieve any
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 224) frequency, within limits, requested by the governor. A frequency does not have
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 225) to be strictly associated with a P-state.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 226)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 227) 2.2 cpuinfo_transition_latency:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 228) -------------------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 229) The cpuinfo_transition_latency field is 0. The PCC specification does
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 230) not include a field to expose this value currently.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 231)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 232) 2.3 cpuinfo_cur_freq:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 233) ---------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 234) A) Often cpuinfo_cur_freq will show a value different than what is declared
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 235) in the scaling_available_frequencies or scaling_cur_freq, or scaling_max_freq.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 236) This is due to "turbo boost" available on recent Intel processors. If certain
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 237) conditions are met the BIOS can achieve a slightly higher speed than requested
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 238) by OSPM. An example:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 239)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 240) scaling_cur_freq : 2933000
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 241) cpuinfo_cur_freq : 3196000
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 242)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 243) B) There is a round-off error associated with the cpuinfo_cur_freq value.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 244) Since the driver obtains the current frequency as a "percentage" (%) of the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 245) nominal frequency from the BIOS, sometimes, the values displayed by
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 246) scaling_cur_freq and cpuinfo_cur_freq may not match. An example:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 247)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 248) scaling_cur_freq : 1600000
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 249) cpuinfo_cur_freq : 1583000
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 250)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 251) In this example, the nominal frequency is 2933 MHz. The driver obtains the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 252) current frequency, cpuinfo_cur_freq, as 54% of the nominal frequency:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 253)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 254) 54% of 2933 MHz = 1583 MHz
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 255)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 256) Nominal frequency is the maximum frequency of the processor, and it usually
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 257) corresponds to the frequency of the P0 P-state.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 258)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 259) 2.4 related_cpus:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 260) -----------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 261) The related_cpus field is identical to affected_cpus.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 262)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 263) affected_cpus : 4
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 264) related_cpus : 4
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 265)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 266) Currently, the PCC driver does not evaluate _PSD. The platforms that support
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 267) PCC do not implement SW_ALL. So OSPM doesn't need to perform any coordination
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 268) to ensure that the same frequency is requested of all dependent CPUs.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 269)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 270) 3. Caveats:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 271) -----------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 272) The "cpufreq_stats" module in its present form cannot be loaded and
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 273) expected to work with the PCC driver. Since the "cpufreq_stats" module
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 274) provides information wrt each P-state, it is not applicable to the PCC driver.
Orange Pi5 kernel
Deprecated Linux kernel 5.10.110 for OrangePi 5/5B/5+ boards
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