Enable i2c-hid interface for touchpad

src/mainboard/system76/lemp9/Kconfig

@@ -4,6 +4,7 @@ config BOARD_SPECIFIC_OPTIONS
 	def_bool y
 	select ADD_FSP_BINARIES
 	select BOARD_ROMSIZE_KB_16384
+	select DRIVERS_I2C_HID
 	select EC_ACPI
 	select HAVE_ACPI_RESUME
 	select HAVE_ACPI_TABLES

src/mainboard/system76/lemp9/devicetree.cb

@@ -2,6 +2,11 @@ chip soc/intel/cannonlake
 	# Lock Down
 	register "common_soc_config" = "{
 		.chipset_lockdown = CHIPSET_LOCKDOWN_COREBOOT,
+		.i2c[0] = {
+			.speed = I2C_SPEED_FAST,
+			.rise_time_ns = 80,
+			.fall_time_ns = 110,
+		},
 	}"
 
 	# Send an extra VR mailbox command for the PS4 exit issue
@@ -33,6 +38,22 @@ chip soc/intel/cannonlake
 	#register "enable_c6dram" = "1"
 
 # FSP Silicon (soc/intel/cannonlake/fsp_params.c)
+	# Serial I/O
+	register "SerialIoDevMode" = "{
+		[PchSerialIoIndexI2C0] = PchSerialIoPci,
+		[PchSerialIoIndexI2C1] = PchSerialIoDisabled,
+		[PchSerialIoIndexI2C2] = PchSerialIoPci,
+		[PchSerialIoIndexI2C3] = PchSerialIoDisabled,
+		[PchSerialIoIndexI2C4] = PchSerialIoDisabled,
+		[PchSerialIoIndexI2C5] = PchSerialIoDisabled,
+		[PchSerialIoIndexSPI0] = PchSerialIoDisabled,
+		[PchSerialIoIndexSPI1] = PchSerialIoDisabled,
+		[PchSerialIoIndexSPI2] = PchSerialIoDisabled,
+		[PchSerialIoIndexUART0] = PchSerialIoDisabled,
+		[PchSerialIoIndexUART1] = PchSerialIoDisabled,
+		[PchSerialIoIndexUART2] = PchSerialIoPci,
+	}"
+
 	# SATA
 	register "SataMode" = "Sata_AHCI"
 	register "SataSalpSupport" = "0"
@@ -195,7 +216,16 @@ chip soc/intel/cannonlake
 			device pci 14.3 on  end # CNVi wifi
 		#end
 		device pci 14.5 off end # SDCard
-		device pci 15.0 off end # I2C #0
+		device pci 15.0 on
+			chip drivers/i2c/hid
+				register "generic.hid" = ""PNP0C50""
+				register "generic.desc" = ""ELAN Touchpad""
+				register "generic.irq" = "ACPI_IRQ_EDGE_LOW(GPP_B3_IRQ)"
+				register "generic.probed" = "1"
+				register "hid_desc_reg_offset" = "0x01"
+				device i2c 15 on end
+			end
+		end # I2C #0 
 		device pci 15.1 off end # I2C #1
 		device pci 15.2 off end # I2C #2
 		device pci 15.3 off end # I2C #3

src/mainboard/system76/lemp9/gpio.h

@@ -152,8 +152,8 @@ static const struct pad_config gpio_table[] = {
 		PAD_CFG_NC(GPP_B2),
 
 	// CPU Misc
-		// GPP_B3
-		_PAD_CFG_STRUCT(GPP_B3, 0x80100100, 0x0000),
+		// GPP_B3 (touchpad interrupt)
+		PAD_CFG_GPI_APIC(GPP_B3, NONE, PLTRST, EDGE_SINGLE, INVERT),
 		// NC
 		PAD_CFG_NC(GPP_B4),