docs: Commands to collect some devicetree values

These values were originally comments in every devicetree. Add them here
for now.

docs/adding-a-new-board.md

@@ -73,6 +73,44 @@ Once coreboot is ported, add its configuration.
 cp coreboot/.config models/<model>/coreboot.config
 ```
 
+### devicetree
+
+Some values to set in `devicetree.cb` that are not collected by `generate.sh`.
+
+- Power limits
+```
+sudo cat /sys/class/powercap/intel-rapl:0/constraint_0_power_limit_uw
+sudo cat /sys/class/powercap/intel-rapl:0/constraint_1_power_limit_uw
+```
+
+- Power
+```
+# pmc_bar + GEN_PMCON_A
+sudo devmem2 0xfe001020
+# PchPmSlpS3MinAssert = bits 11:10
+# PchPmSlpS4MinAssert = bits 5:4
+
+# pmc_bar + PM_CFG
+sudo devmem2 0xfe001818
+# PchPmSlpSusMinAssert = bits 19:18
+# PchPmSlpAMinAssert = bits 17:16
+```
+
+- Thermal
+```
+sudo modprobe msr
+sudo rdmsr --bitfield 31:24 --decimal 0x1A2
+```
+
+- LPC
+```
+sudo lspci -s 1f.0 -xxx
+# gen1_dec: 0x84-0x87
+# gen2_dec: 0x88-0x8B
+# gen3_dec: 0x8C-0c8F
+# gen4_dec: 0x90-0x93
+```
+
 ## Porting System76 EC
 
 To port System76 EC firmware to a new board, see the EC documentation.