FM / power

/sys/devices/pci0000:00/0000:00:03.6/pci_bus/0000:0f/power

Name	Size	Mode	Actions
autosuspend_delay_ms	4096	0644	edit dl rm
control	4096	0644	edit dl rm
runtime_active_time	4096	0444	edit dl rm
runtime_status	4096	0444	edit dl rm
runtime_suspended_time	4096	0444	edit dl rm

Edit: /sys/devices/pci0000:00/0000:00:03.6/pci_bus/0000:0f/power/runtime_active_time (4096B)