BrightnessKeys

Automatic handling of brightness keys based on ACPI Specification, Appendix B: Video Extensions.
Requires Lilu 1.2.0 or newer.

Boot arguments

• -brkeysdbg to enable debug printing (available in DEBUG binaries).

Special cases

Typically no DSDT patches are required. Please remove old _Qxx to XQxx ones.
On some models, may be required add ACPI patch _OSI to XOSI and SSDT-XOSI.

Spoiler: On some old ThinkPad models, additional handling may be required.

Here is an example for their "brightness up" EC event.

Method (_Q14, 0, NotSerialized)
{
    If (^HKEY.MHKK (0x8000))
    {
        ^HKEY.MHKQ (0x1010)                // Vendor-specific event: TP_HKEY_EV_BRGHT_UP
    }

    If (NBCF) // Whether
    {
        If (VIGD)
        {
            Notify (^^^VID.LCD0, 0x86)     // Send 0x86 "Increase Brightness" to integrated graphics
        }
        Else
        {
            Notify (^^^PEG.VID.LCD0, 0x86) // Send 0x86 "Increase Brightness" to discrete graphics
        }
    }
    Else
    {
        Local0 = BRLV                      // Local variable to store current brightness level
        If ((Local0 != 0x0F))
        {
            Local0++
            BRLV = Local0
        }

        If (VIGD)
        {
            UCMS (0x16)                    // SMI access for integrated graphics
            BRNS ()
        }
        Else
        {
            VBRC (Local0)                  // SMI access for discrete graphics
        }

        ^HKEY.MHKQ (0x6050)                // Vendor-specific event: TP_HKEY_EV_BACKLIGHT_CHANGED
    }
}

When NBCF is set to zero by default, the method will not notify graphics devices and try to adjust brightness directly. To override that, set NBCF = 0x01 in SSDT hotpatch, or just replace its declaration using a simple patch.

• For DSDT compiled with older iasl, replace Name (NBCF, 0x00) to Name (NBCF, 0x01):
  Find: 08 4E424346 0A 00 // NameOp "NBCF" BytePrefix "00"
  Repl: 08 4E424346 0A 01 // NameOp "NBCF" BytePrefix "01"

• For DSDT compiled with newer iasl, replace Name (NBCF, Zero) to Name (NBCF, One):
  Find: 08 4E424346 00 // NameOp "NBCF" ZeroOp
  Repl: 08 4E424346 01 // NameOp "NBCF" OneOp

Credits

• Apple for macOS
• usr-sse2 for separating this driver from VoodooPS2
• vit9696 for DeviceInfo API from Lilu
• zhen-zen for implementation