Getting-Started-With-ACPI/Laptops/trackpad-methods/manual.md

Fixing Trackpads: Manual

• Checking GPI0
• Edits to the sample SSDT
• Compiling the SSDT
• Wrapping up

Checking GPI0

The first thing which should be checked is the GPI0 device, which is required for VoodooI2C. The best way to check this is working is to use IORegistryViewer.

Here, we can see that VoodooGPIO is attached to GPI0 so no edits are needed for GPI0 and you can skip to the next section.

If VoodooGPIO isn't attached, then you may need to modify the _STA method in the GPI0 device. In that case, you will need to find the GPI0 device in ACPI.

First open your decompiled DSDT you got from Dumping the DSDT and Decompiling and Compiling with either maciASL(if in macOS) or any other text editor if in Windows or Linux(VSCode has an ACPI extension that can also help).

Next search for Device (GPI0). Should give you a result similar to this:

We can see that _STA method, which enables or disable the GPI0 device:

Method (_STA, 0, NotSerialized)
{
    If ((SBRG == Zero))
    {
        Return (Zero)
    }

    If ((GPEN == Zero))
    {
        Return (Zero)
    }

    Return (0x0F)
}

We want the value returned from _STA to be 0x0F to enable the GPI0 device. If either SBRG or GPEN is equal to zero, then zero will be returned and GPI0 will be disabled. Generally, SBRG should not be modified, as modifying it can break the GPI0 device. Only modify the GPEN value if you need to enable the GPI0 device.

Here's some more examples:

What we care about from this is the _STA method:

Method (_STA, 0, NotSerialized)
{
    If ((GPHD == One))
    {
        Return (0x03)
    }

    Return (0x0F)
}

What we want is for this to always return 0x0F when booting macOS, so we want to make an SSDT that will return GPHD == Zero in macOS.

NOTE that you may have the other way around where GPHD needs to be set as One to return 0x0F. And your device name may also be different, don't throw random SSDTs in thinking it'll work

Edits to the sample SSDT

Now that we have our ACPI path, lets grab our SSDT and get to work:

• SSDT-GPI0.dsl

From the first example, we'll want to set GPEN to One to allow it to operate in macOS:

// This is likely already set in the SSDT-GPIO you just downloaded
If (_OSI ("Darwin"))
{
    GPEN = One
}

For the second example, you'd want to remove GPEN and use the below:

If (_OSI ("Darwin"))
{
    GPHD = Zero
}

You will want to test the SSDT at this point by compiling the SSDT! and adding it to your config.plist. VoodooI2C should now be attached to the GPI0 device as shown at the top of the GPI0 section.

Enabling Trackpad

Often times, the I2C devices check to see if they are running in Windows before enabling themselves. Similarly to the GPI0 device, these devices contain a _STA method. For example, this is the I2C1 device below:

The part we care about is the _STA method:

Method (_STA, 0, NotSerialized)  // _STA: Status
{
    Return (LSTA (SMD1))
}

In this case, _STA is referring to another method, LSTA. If we search for Method (LSTA, we'll see the below:

Method (LSTA, 1, Serialized)
{
    If (((Arg0 == 0x00) || (Arg0 == 0x03)))
    {
        Return (0x00)
    }

    If (CondRefOf (OSYS))
    {
        If ((OSYS < 0x07DC))
        {
            Return (0x00)
        }
    }

    Return (0x0F)
}

LSTA checks Arg0 and OSYS. Arg0 is the value passed in from where it's called. In this example, _STA passes in SMD1 as Arg0. This value should already be correct. The value which we should check is OSYS, which is a value which stores information about the current OS running. We will want to look for any place in which OSYS is set (OSYS = 0x07DC for example). In this DSDT, this is set under \_SB.PCI0._INI as shown below:

There are various checks for many different versions of Windows, but there is no check for Darwin (which Apple's ACPI usually checks for). We generally want to set OSYS to the value for the latest version of Windows in order to enable the most features. In this case, the latest version of Windows is "Windows 2015", or Windows 10. This means that we should set OSYS to 0x07DF. Notice that this value is greater than the OSYS < 0x07DC value being checked for earlier, which means that the check in LSTA should return 0x0F now.

Before:

If (_OSI ("Darwin"))
{
    GPEN = One
}

After:

If (_OSI ("Darwin"))
{
    GPEN = One
    OSYS = 0x07DF
}

Note that Windows will also return true for checks of earlier versions of the OS. For example, Windows 7 would return true for "Windows 2000" through "Windows 2009", but not any version after. This is important as some features are only enabled in earlier Windows checks. For example, WNTF = 0x01 allows DYTC thermal management to work on newer Thinkpads, though this only gets set in the check for "Windows 2001". You will need to check your own DSDT and see what values it sets and where they are used.

Wrapping up

Once you're done making your SSDT, either head to the next page to finish the rest of the SSDTs or head here if you're ready to wrap up:

• Cleanup