SGMicro SGM3140 (camera flash driver)

Identity

Status — ● working

DTS overlay in tree (src/sys/dts/arm64/overlays/sgm3140.dtso) wires both FLASH_EN and FLASH_TORCH as gpioled(4) consumers via a sibling compatible = "gpio-leds" node — FreeBSD has no driver for the upstream sgmicro,sgm3140 compatible string, so we reuse the existing two GPIOs through the standard gpio-leds binding instead.

Verified live on 2026-05-03 (kernel #140+, head b7ec39b): /dev/led/flash and /dev/led/torch exist; echo 1 > /dev/led/flash turns the rear flashlight on continuously (torch mode), and /dev/led/flash + /dev/led/torch together produce a visible camera strobe at 250 ms (the bench’s 80 ms pulse is real but too brief for the eye). The overlay had to be added to sys/modules/dtb/rockchip/Makefile ( b7ec39b dtb: build sgm3140 overlay as part of the rockchip dtb modules ) so buildkernel actually emits sgm3140.dtbo, and the phone’s fdt_overlays line in /boot/loader.conf had to grow sgm3140 beyond the original bcm-hostwake.

The part itself is a two-GPIO state machine, not a sensor. Linux’s leds-sgm3140 driver treats the GPIO named enable as the chip enable and the GPIO named flash as the mode/strobe line: torch/brightness mode is enable=1, flash=0; flash/strobe mode is enable=1, flash=1. Our gpioled overlay exposes those two raw lines as /dev/led/flash (enable) and /dev/led/torch (flash/mode), which makes this useful as a flashlight even though the cameras themselves are person-years out.

Driver

• Our tree: src/sys/dts/arm64/overlays/sgm3140.dtso — pure DT overlay, no C driver. Adds a root-level compatible = "gpio-leds" node with two children (flash, torch) that bind to the in-tree gpioled(4) driver.
• Linux mainline: drivers/leds/leds-sgm3140.c — small driver registering an LED class device + V4L2 flash subdev. The LED-class side is the relevant reference for FreeBSD; the V4L2 side is moot until cameras land. Linux uses flash-gpios + enable-gpios properties on its own compatible; we expose the same two GPIOs through the generic gpio-leds binding instead, since FreeBSD has no sgmicro,sgm3140 driver.

No I2C, no clocks, no regulators beyond what the rest of the camera area already provides; the base DTS already has the flash_pins pinctrl group, which our overlay reuses.

Parity verification

• dmesg should show two gpioled instances at attach (one per child node), e.g. gpioledN: <GPIO LED> on simplebus0.

• ls /dev/led/ should list both flash and torch.

• Use the checked-in bounded bench helper instead of hand-writing GPIOs:

  mise run debug:flash:sgm3140 -- status
  mise run debug:flash:sgm3140 -- torch
  mise run debug:flash:sgm3140 -- flash

  torch defaults to 300 ms; flash defaults to 80 ms and is capped at 250 ms by the wrapper. Override with TORCH_MS=500 or FLASH_MS=100 if the first pass is too short to see.

• The helper treats /dev/led/flash as the SGM3140 enable line and /dev/led/torch as the flash/mode line: torch mode sets flash=1, torch=0; flash mode sets flash=1, torch=1. Both paths trap exit and force both LED nodes low.

• Falsifier — no /dev/led/ entries after attach: the gpioled consumer didn’t bind. Most likely causes: the overlay didn’t actually merge (check kenv | grep fdt_overlays and the bootverbose FDT log), or the GPIO bank/offset is wrong (re-derive from RK_PC6 = 2*8+6 = 22, RK_PA3 = 0*8+3 = 3, both active-high).

• Falsifier — /dev/led/{flash,torch} exist but the LED stays dark: polarity is inverted, flash_pins isn’t being applied so the pads are still in their default mux, or the mode/enable interpretation is wrong. Sanity-check with a multimeter on the SGM3140 EN/TORCH pins.

Open work

• Decide whether to expose a single combined node with a mode sysctl (flash pulse vs torch sustained) if raw /dev/led/flash + /dev/led/torch proves too awkward for userland.
• Smoke-test current draw on the bench before relying on it heavily — the SGM3140 will happily pull more than the battery wants if both GPIOs are misdriven (especially FLASH_EN high without the strobe path correctly arbitrated).

Related

• What’s next: finish WiFi, then modem — camera roadmap context.
• IMX258 component reference — the camera that would eventually use the flash.
• Hardware reference — chip manifest.