aaronlu

            Device (PMIC)
            {
                Name (_ADR, Zero)  // _ADR: Address
                Name (_HID, "INT33FD")  // _HID: Hardware ID
                Name (_CID, "INT33FD")  // _CID: Compatible ID
                Name (_DDN, "PMIC GPIO Controller")  // _DDN: DOS Device Name
                Name (_HRV, 0x02)  // _HRV: Hardware Revision
                Name (_UID, One)  // _UID: Unique ID
                Name (_DEP, Package (0x01)  // _DEP: Dependencies
                {

aaronlu

A typical ASL code for the backlight control method _BCM with Intel
graphics card is as follows:

        Method (_BCM, 1, NotSerialized)
        {
            If (BRNC)
            {
                AINT (One, Arg0)
            }
            Else

aaronlu

1st stage

start_kernel
  -> time_init -> set late_time_init to x86_late_time_init
    -> late_time_init => x86_late_time_init
      -> x86_init.timers.timer_init => hpet_timer_init
        -> hpet_enable
          -> hpet_legacy_clockevent_register()
             the clock_event_device is registered as a per-cpu clock event device
      -> tsc_init

aaronlu

i. Some background on backlight control:

For a laptop, there usually are three sources to control backlight:
one from video module's ACPI interface;
one from x86 platform driver's ACPI interface;
one from GPU driver's native interface.

All of them will register a backlight device, which will create a sysfs
interface under /sys/class/backlight for users to control, they are
identified by their type:

aaronlu

i. Some background on backlight control:

For a laptop, there usually are three sources to control backlight:
one from video module's ACPI interface;
one from x86 platform driver's ACPI interface;
one from GPU driver's native interface.

All of them will register a backlight device, which will create a sysfs
interface under /sys/class/backlight for users to control, they are
identified by their type: