/sys/class/devfreq-event
| Field | Value |
|---|---|
| Subsystem | devfreq-event framework (event counters feeding devfreq governors), PM subsystem; implementation file not in cached tree |
| Config gate | not verifiable from the cached sources (cached tree has no Kconfig or driver files); class absent on the live host |
| ABI documentation | Documentation/ABI/testing/sysfs-class-devfreq-event (3 What entries) |
| Since | January 2017 (all entries; no KernelVersion line stated in the file) |
| Live (5.10.134 host) | class absent: not in live-sys/class-list.txt, no /sys/class/devfreq-event |
| Ledger ID | SYSC-devfreq-event |
What it represents
One directory per devfreq-event object, named event<x> with a unique number x. A devfreq-event device is a monitored resource - typically a set of hardware performance counters (DDRC load, bus utilization, PMU blocks) - that devfreq governors read to decide frequency changes. The class is the sysfs handle for enumerating those counters and their enable state.
Relationship to the device model
Each event<x> directory is a class view of a devfreq-event device registered by a platform driver. The event objects are consumed by devfreq through the kernel API; sysfs only exposes the name and the enable reference count, so userspace can see which measurement blocks exist and whether any governor is currently using them. Unlike devfreq there is no control surface here: no file selects an event or configures it. The class can also exist independently of any devfreq consumer - the ABI describes the objects as a place for devfreq-event variables, with the enable count simply staying at zero when no governor has enabled the event.
Attributes
| Attribute | R/W | Unit/format | Conditional? | Source |
|---|---|---|---|---|
event<x>/ | – | directory per devfreq-event object | always | ABI, January 2017 |
event<x>/name | RO | name of the devfreq-event object | always | ABI, January 2017 |
event<x>/enable_count | RO | integer reference count; > 0 means enabled | always | ABI, January 2017 |
Safety and writes
All three documented paths are read-only; there is nothing to write and no permission hazard. The enable reference count is kernel-managed: it increases when a consumer (a devfreq governor) enables the event and decreases on disable, so a nonzero value only means “in use by the kernel right now”. No ABI documentation exists for any write access to this class.