On Sun, Feb 19, 2023 at 12:20:06AM +1100, Orlando Chamberlain wrote: > --- a/drivers/platform/x86/apple-gmux.c > +++ b/drivers/platform/x86/apple-gmux.c > @@ -28,15 +28,17 @@ > * DOC: Overview > * > * gmux is a microcontroller built into the MacBook Pro to support dual GPUs: > - * A `Lattice XP2`_ on pre-retinas, a `Renesas R4F2113`_ on retinas. > + * A `Lattice XP2`_ on pre-retinas, a `Renesas R4F2113`_ on pre-T2 retinas. > + * The chip used on T2 Macs is not known. I've just taken a look at the schematics of the MBP16,1 and it turns out that T2 *is* the gmux. The chip is called H9M. The interaction with the OS is through that MMIO area. There's a GPIO expander attached to T2 via I2C (NXP PCAL6524), probably because they didn't have enough GPIO pins available on T2 itself. The GPIO expander enables/disables the voltage regulators of the discrete GPU, hence can cut power to it. It also drives panel power and has a GPIO to switch the mux. The mux is an NXP CBTL06142 as on previous models. Thanks, Lukas
