Hi @SeanH I am also interested in accessing the GPIO from Windows. I think you’re onto something with the RHPROXY driver.
I want to get access to the GPIO pins so I was looking at the Appendix A - Raspberry Pi ASL Listing section.
I suggest you run RWEverything and get a ACPI dump of the DSDT tables. You will see there are following entries:
_SB.PCI0.URT1 // Intel(R) HS-UART Controller #1
_SB.PCI0.URT2 // Intel(R) HS-UART Controller #2
_SB.PCI0.URT3 // Intel(R) HS-UART Controller #3
_SB.PCI0.URT4 // Intel(R) HS-UART Controller #4
_SB.PCI0.SPI1 // Intel(R) SPI Controller #1
_SB.PCI0.SPI2 // Intel(R) SPI Controller #2
_SB.PCI0.SPI3 // Intel(R) SPI Controller #3
_SB.PCI0.I2C0 // Intel(R) I2C Controller #0
_SB.PCI0.I2C1 // Intel(R) I2C Controller #1
_SB.PCI0.I2C2 // Intel(R) I2C Controller #2
_SB.PCI0.I2C3 // Intel(R) I2C Controller #3
_SB.PCI0.I2C4 // Intel(R) I2C Controller #4
_SB.PCI0.I2C5 // Intel(R) I2C Controller #5
_SB.PCI0.I2C6 // Intel(R) I2C Controller #6
_SB.PCI0.I2C7 // Intel(R) I2C Controller #7
_SB.PCI0.GPO0 // General Purpose Input/Output (GPIO) Controller - North
_SB.PCI0.GPO1 // General Purpose Input/Output (GPIO) Controller - Northwest
_SB.PCI0.GPO2 // General Purpose Input/Output (GPIO) Controller - Audio
_SB.PCI0.GPO3 // General Purpose Input/Output (GPIO) Controller - SCC
Perhaps this post by @zerrofour4 will help construct an ASL for it?