docs: Add ABI documentation for intel_pmt feature directories

What:          /sys/class/intel_pmt/features-<PCI BDF>/

Date:          2025-04-24

KernelVersion: 6.16

Contact:       david.e.box@linux.intel.com

Description:

               The `features-<PCI BDF>/` directory represents the "features"

               capability exposed by Intel PMT (Platform Monitoring Technology)

               for the given PCI device.

               Each directory corresponds to a PMT feature and contains

               attributes describing the available telemetry, monitoring, or

               control functionalities.

Directory Structure:

  /sys/class/intel_pmt/features-<PCI BDF>/

  ├── accelerator_telemetry/		# Per-accelerator telemetry data

  ├── crash_log/			# Contains system crash telemetry logs

  ├── per_core_environment_telemetry/	# Environmental telemetry per core

  ├── per_core_performance_telemetry/	# Performance telemetry per core

  ├── per_rmid_energy_telemetry/	# Energy telemetry for RMIDs

  ├── per_rmid_perf_telemetry/		# Performance telemetry for RMIDs

  ├── tpmi_control/			# TPMI-related controls and telemetry

  ├── tracing/				# PMT tracing features

  └── uncore_telemetry/			# Uncore telemetry data

Common Files (Present in all feature directories):

  caps

    - Read-only

    - Lists available capabilities for this feature.

  guids

    - Read-only

    - Lists GUIDs associated with this feature.

Additional Attributes (Conditional Presence):

  max_command_size

    - Read-only

    - Present if the feature supports out-of-band MCTP access.

    - Maximum supported MCTP command size for out-of-band PMT access (bytes).

  max_stream_size

    - Read-only

    - Present if the feature supports out-of-band MCTP access.

    - Maximum supported MCTP stream size (bytes).

  min_watcher_period_ms

    - Read-only

    - Present if the feature supports the watcher API.

      The watcher API provides a writable control interface that allows user

      configuration of monitoring behavior, such as setting the sampling or

      reporting interval.

    - Minimum supported time period for the watcher interface (milliseconds).

  num_rmids

    - Read-only

    - Present if the feature supports RMID (Resource Monitoring ID) telemetry.

      RMIDs are identifiers used by hardware to track and report resource usage,

      such as memory bandwidth or energy consumption, on a per-logical-entity

      basis (e.g., per core, thread, or process group).

    - Maximum number of RMIDs tracked simultaneously.

Example:

For a device with PCI BDF `0000:00:03.1`, the directory tree could look like:

  /sys/class/intel_pmt/features-0000:00:03.1/

  ├── accelerator_telemetry/

  │   ├── caps

  │   ├── guids

  │   ├── max_command_size

  │   ├── max_stream_size

  │   ├── min_watcher_period_ms

  ├── crash_log/

  │   ├── caps

  │   ├── guids

  │   ├── max_command_size

  │   ├── max_stream_size

  ├── per_core_environment_telemetry/

  │   ├── caps

  │   ├── guids

  │   ├── max_command_size

  │   ├── max_stream_size

  │   ├── min_watcher_period_ms

  ├── per_rmid_energy_telemetry/

  │   ├── caps

  │   ├── guids

  │   ├── max_command_size

  │   ├── max_stream_size

  │   ├── min_watcher_period_ms

  │   ├── num_rmids

  ├── tpmi_control/

  │   ├── caps

  │   ├── guids

  ├── tracing/

  │   ├── caps

  │   ├── guids

  ├── uncore_telemetry/

  │   ├── caps

  │   ├── guids

  │   ├── max_command_size

  │   ├── max_stream_size

  │   ├── min_watcher_period_ms

Notes:

  - Some attributes are only present if the corresponding feature supports

    the capability (e.g., `max_command_size` for MCTP-capable features).

  - Features supporting RMIDs include `num_rmids`.

  - Features supporting the watcher API include `min_watcher_period_ms`.

  - The `caps` file provides additional information about the functionality

    of the feature.

Example 'caps' content for the 'tracing' feature:

  /sys/class/intel_pmt/features-0000:00:03.1/

  ├── tracing/

  │   ├── caps

	telemetry                                Available: No

	watcher                                  Available: Yes

	crashlog                                 Available: No

	streaming                                Available: No

	threashold                               Available: No

	window                                   Available: No

	config                                   Available: Yes

	tracing                                  Available: No

	inband                                   Available: Yes

	oob                                      Available: Yes

	secure_chan                              Available: No

	pmt_sp                                   Available: Yes

	pmt_sp_policy                            Available: Yes

	mailbox                                  Available: Yes

	bios_lock                                Available: Yes

M:	David E. Box <david.e.box@linux.intel.com>

S:	Supported

F:	Documentation/ABI/testing/sysfs-class-intel_pmt

F:	Documentation/ABI/testing/sysfs-class-intel_pmt-features

F:	drivers/platform/x86/intel/pmt/

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