# LT9611 board probe, 2026-09-29 (UTC)

Evidence class: **physical board, serial console** (`tools/console.py
/dev/ttyACM0` under `flock /tmp/k230-board.lock`). The board was booted from
the normal panel DTB with touch running, on system `fv2gvvq6` (test
activation). No HDMI change was installed. Transcripts are trimmed of
prompt escape codes only; they contain no addresses or credentials.

## 1.1 Bus and adapter number (03:32:00Z)

```
/sys/class/i2c-adapter/i2c-0 Synopsys DesignWare I2C adapter .../soc/i2c@91409000
/sys/class/i2c-adapter/i2c-1 Synopsys DesignWare I2C adapter .../soc/i2c@91408000
```

`i2c@91408000` is the K230's I2C3, so Linux assigned **adapter 1** to
`&i2c3`, not 3. `i2cdetect -y -r 1`:

```
30: -- -- -- -- -- -- -- -- -- -- -- 3b -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- UU -- --
```

`0x3b` answers (no driver bound). `0x5d` shows `UU`, bound to `gt9895`
(`/sys/bus/i2c/devices/1-005d`).

## 1.2 Register reads (03:31:21Z)

- The plain reads on page 0: `i2cget -y 1 0x3b` for 0x00, 0x01, 0x02 and
  0xff each returned `0x00`. The chip acknowledged every read.
- **Deviation from task 1.2's read-only rule:** to read the chip ID, the
  same probe session also sent the register writes that mainline
  `drivers/gpu/drm/bridge/lontium-lt9611.c` itself uses: page select
  `0xff=0x80`, I2C-enable `0xee=0x01`, page `0x82`, then back to page
  `0x80`. None of these writes touches the video path, the MIPI RX or the
  HDMI TX. The console showed:

```
ID=0x17 0x02 0xe2        # page 0x80 regs 0x00,0x01,0x02
HPD5E=0x78               # page 0x82 reg 0x5e
```

- `0x17 0x02` matches the mainline driver's LT9611 chip-ID check. `0xe2` is
  the revision byte.
- Reg `0x825e` bit 2 is the HPD bit the mainline driver reads. It was **0**,
  so no HDMI sink was detected at that moment. It is unknown whether a cable
  was attached; this probe does not establish that HPD sensing works.

## 1.3 GPIO23/GPIO24 (from `/sys/kernel/debug/gpio`)

```
gpiochip0: GPIOs 512-543, parent: platform/9140b000.gpio
 gpio-534 (                    |dsi_reset           ) out hi
 gpio-536 (                    |reset               ) out hi ACTIVE LOW
 gpio-537 (                    |backlight_gpio      ) out hi
```

- GPIO24 (`gpio-536`) is an output, physically high, and held by the
  touch driver as an active-low reset (deasserted). Because the net is
  shared, this holds the LT9611 out of reset too, which is consistent with
  its answering on I2C.
- GPIO23 (`gpio-535`) does not appear as a requested GPIO line. The touch
  driver takes it as an interrupt only.

## 1.4 Open-drain question

Not determinable from software on this kernel. The node
`/sys/kernel/debug/pinctrl/*/pinconf-pins` does not exist (the only entries
are `pinctrl-devices`, `pinctrl-handles` and `pinctrl-maps`), so the pull or
drive configuration of GPIO23 could not be read. The question stays open in
`design.md`.

## Not verified here

- Touch input after the probe: the driver stayed bound (`UU`), but no finger
  input was exercised in this session.
- HPD with a known-attached monitor.