[PATCH v9 0/5] CPUFreq driver using CPPC methods

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CPPC:
====

CPPC (Collaborative Processor Performance Control) is a new way to control CPU
performance using an abstract continous scale as against a discretized P-state scale
which is tied to CPU frequency only. It is defined in the ACPI 5.0+ spec. In brief,
the basic operation involves:
- OS makes a CPU performance request. (Can provide min and max tolerable bounds)

- Platform (such as BMC) is free to optimize request within requested bounds depending
on power/thermal budgets etc.

- Platform conveys its decision back to OS

The communication between OS and platform occurs through another medium called (PCC)
Platform communication Channel. This is a generic mailbox like mechanism which includes
doorbell semantics to indicate register updates. See drivers/mailbox/pcc.c

This patchset introduces a CPPC based CPUFreq driver that works with existing governors
such as ondemand. The CPPC table parsing and the CPPC communication semantics are
abstracted into separate files to allow future CPPC based drivers to implement their
own governors if required.

Initial patchsets included an adaptation of the PID governor from intel_pstate.c. However
recent experiments led to extensive modifications of the algorithm to calculate CPU
busyness. Until it is verified that these changes are worthwhile, the existing governors
should provide for a good enough starting point for ARM64 servers.

Finer details about the PCC and CPPC spec are available in the latest ACPI 5.1
specification.[2]

Testing:
=======

This was tested on an SBSA compatible ARMv8 server with CPPCv2
firmware running on a remote processor. I verified that each CPUs
performance limits were detected and that new performance requests
were made by the on-demand governor proportional to the load on each
CPU. I also verified that using the acpi_processor driver correctly
maps the physical CPU ids to logical CPU ids, which helps in picking
up the proper _CPC details from a processor object, in the case where
CPU physical ids may not be contiguous.

Changes since V8:
- Fixed up several debug prints, return types and comments.
- Simplified read/write ops using existing ACPI core API.
- Removed ->get() from cpufreq driver for now.
- Fixed bug introduced by copy-paste err in set_perf.

Changes since V7:
- Simplied new kconfig options for PSS and idle.
- Separated patch to enable acpi processor on ARM64.
- Removed redundant kconfig cross deps on PCC.
- Decoupled processor_perflib from new PSS kconfig option.

Changes since V6:
- Separated PSS and CST from ACPI processor driver in two patches.
- Made new Kconfig symbols auto selectable from Arch Kconfigs.

Changes since V5:
- Checkpatch cleanups.
- Change pss_init to pss_perf_init. Rec by Srinivas Pandruvada.
- Explicit comment explaining why postcore_initcall to pcc mailbox.
- Fold acpi_processor_syscore_init/exit into CONFIG_ACPI_CST.
- Added patch with dummy functions used by ACPI_HOTPLUG_CPU.

Changes since V4:
- Misc cleanups. Addressed feedback from Rafael.
- Made acpi_processor.c independent of C-states, P-states and others.
- Per CPU scanning for _CPC is now made from acpi_processor.c
- Added new Kconfig options for legacy C states and P states to enable future
support for newer alternatives as defined in the ACPI spec 6.0.

Changes since V3:
- Split CPPC backend methods into separate files.
- Add frontend driver which plugs into existing CPUfreq governors.
- Simplify PCC driver by moving communication space mapping and read/write
	into client drivers.

Changes since V2:
- Select driver if !X86, since intel_pstate will use HWP extensions instead.
- Added more comments.
- Added Freq domain awareness and PSD parsing.

Changes since V1:
- Create a new driver based on Dirks suggestion.
- Fold in CPPC backend hooks into main driver.

Changes since V0: [1]
- Split intel_pstate.c into a generic PID governor and platform specific backend.
- Add CPPC accessors as PID backend.

[1] - http://lwn.net/Articles/608715/
[2] - http://www.uefi.org/sites/default/files/resources/ACPI_5_1release.pdf
[3] - https://patches.linaro.org/40705/

Ashwin Chaugule (5):
  ACPI: Introduce CPU performance controls using CPPC
  CPPC: Add a CPUFreq driver for use with CPPC
  ACPI: Add weak routines for ACPI CPU Hotplug
  CPPC: Probe for CPPC tables for each ACPI Processor object
  ACPI: Allow selection of the ACPI processor driver for ARM64

 drivers/acpi/Kconfig            |  20 +-
 drivers/acpi/Makefile           |   1 +
 drivers/acpi/acpi_processor.c   |  18 +
 drivers/acpi/cppc_acpi.c        | 755 ++++++++++++++++++++++++++++++++++++++++
 drivers/acpi/processor_driver.c |   6 +
 drivers/cpufreq/Kconfig.arm     |  17 +
 drivers/cpufreq/Makefile        |   2 +
 drivers/cpufreq/cppc_cpufreq.c  | 169 +++++++++
 include/acpi/cppc_acpi.h        | 138 ++++++++
 include/acpi/processor.h        |  14 +
 10 files changed, 1137 insertions(+), 3 deletions(-)
 create mode 100644 drivers/acpi/cppc_acpi.c
 create mode 100644 drivers/cpufreq/cppc_cpufreq.c
 create mode 100644 include/acpi/cppc_acpi.h

-- 
1.9.1

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