Dell XPS 15 9560 (1.2.5) NVRAM edits

xps_9560_ifr.txt

# Set Intel(R) Speed Shift Technology to Enabled
setup_var 0x4BC 0x1
# Set CFG Lock to Disabled
setup_var 0x4ED 0x0
# Set Above 4GB MMIO BIOS assignment to Enabled
# setup_var 0x79A 0x1

# Set EHCI Hand-off to Disabled
# setup_var 0x2 0x0
# Set XHCI Hand-off to Disabled
# setup_var 0x1B 0x0

# Set Low Power S0 Idle Capability to Enabled
setup_var 0x13 0x1

# Set DVMT Total Gfx Mem to MAX
# setup_var 0x796 0x3

# Set Overclocking Lock to Disabled
# setup_var 0x59C 0x0
# Set OverClocking Feature to Enabled
setup_var 0x65C 0x1
# Set XTU Interface to Enabled
setup_var 0x65D 0x1

# Set Core Voltage Offset Prefix to Negative
setup_var 0x664 0x1
# Set Core Voltage Offset to -120 mV
setup_var 0x662 0x78

# Set Uncore Voltage Offset Prefix to Negative
setup_var 0x865 0x1
# Set Uncore Voltage Offset to -100 mV
setup_var 0x863 0x64

# Set GT Voltage Offset Prefix to Negative
setup_var 0x86D 0x1
# Set GT Voltage Offset to -100 mV
setup_var 0x86B 0x64

# Set GT Unsliced Voltage Offset Prefix to Negative
setup_var 0x876 0x1
# Set GT Unsliced Voltage Offset to -100 mV
setup_var 0x874 0x64

# Set PCI Express Root Port 13 to Disabled
setup_var 0x95A 0x0

# DCI killed in recent BIOS version?
# chipsec -m chipsec.modules.common.debugenabled reports DCI Debug is disabled even after setting these
# Set Debug Interface to Enabled
# setup_var 0x59D 0x1
# Set Debug Interface Lock to Disabled
# setup_var 0x59E 0x0
# Set Direct Connect Interface to Enabled
# setup_var 0x59F 0x1
# Set DCI enable (HDCIEN) to Enabled
# setup_var 0x899 0x1
# Set TraceHub Enable Mode to Host Debugger
# setup_var 0xEAF 0x2

Unfortunately the bit is reset upon reboot. The only way would be via SPI flash with physical access to the chip using a programmer.