Diary: keyboard pct13x2 found in vendor DTS

DIARY.md

@@ -456,3 +456,45 @@ The 0009 patch needs to add:
 - `power-domains` to edp1, vop, and hdptxphy1
 - `assigned-clocks`/`assigned-clock-parents` to vop
 - `rockchip,pmu` phandle to vop
+
+## Day 2 Very Late Night: Keyboard Investigation
+
+### pct13x2 Identified from Vendor Kernel
+
+The CoolPi vendor kernel (coolpi-george/coolpi-kernel, branch linux-6.1-stan-rkr5.1)
+has the full GenBook DTS at \`rk3588-cpcm5-genbook.dts\`:
+
+**Keyboard (pct13x2):**
+- Bus: I2C5 (0xFEAD0000), pinctrl i2c5m3_xfer
+- Address: 0x2C
+- Compatible: \"hid-over-i2c\" (generic driver)
+- HID descriptor register: 0x0020
+- Interrupt: GPIO1_D6, active low
+- Power: dedicated 5V regulator via GPIO1_A7 (vcc5v0_keyboard)
+
+**Touchpad (g7500):**
+- Bus: I2C4 (0xFEAC0000), pinctrl i2c4m3_xfer
+- Address: 0x10
+- HID descriptor: 0x0001
+- Interrupt: GPIO1_A1, active low
+
+**Battery gauge (CW2015):**
+- Bus: I2C4, address 0x62
+
+**Key insight:** The keyboard needs vcc5v0_keyboard regulator enabled
+(GPIO1_A7 high) before it responds on I2C.
+
+### Sandbox Testing Attempt
+
+Built U-Boot sandbox with the HID-over-I2C driver (patch 0006) and a
+custom I2C emulator. The emulator responds to HID descriptor reads
+with a standard boot keyboard descriptor. 
+
+The sandbox binary builds and runs, but integrating the emulator into
+the sandbox DTS requires more plumbing work. Saved for a future session.
+
+The driver code itself looks correct — the I2C HID protocol implementation
+follows the Microsoft HID-over-I2C v1.0 spec. The real risk is:
+1. Keyboard power regulator not enabled (GPIO1_A7)
+2. Interrupt GPIO not configured correctly
+3. pct13x2 might have non-standard HID quirks