Hi, I'm new with kernel development so I might have done something stupid during my troubleshooting procedure. I'm trying to make working the Ambient Light Sensor on my old Chromebook, this was working up to 4.15 but then something broke in the chromeos_laptop driver. So now the people that are running an alternative Chromebook firmware are using ACPI to load the right modules instead of using the google SMBios table. My first step was to create the ACPI node on coreboot with the i2c hardware information. The ALS chip is the ISL29018 and the right module should be this one: https://elixir.bootlin.com/linux/v5.0.21/source/drivers/iio/light/isl29018.c#L810 According to tho the ACPI table of the driver the _HID should be "ISL29018" we have created the DSDT: https://github.com/MrChromebox/coreboot/blob/5a16469c9fb4131f04b2bc56da03fab0f2faf1bc/src/mainboard/google/slippy/variants/peppy/include/variant/acpi/mainboard.asl#L163 The module is loaded, but nothing happens, so I have started with ftrace to see if there was something wrong with the driver itself and after some more tests I also started to build my own kernel with lots of printk to know the parameters. What I've discovered so far is: i2c_device_probe() is not even called. __acpi_match_device() fails to find a proper match. It is not scanning the right ACPI/PNP from the DSDT. On the i2c bus the device also has an Atmel touchscreen. It tries to match the Atmel TS, not the ALS. (It fails the check here, https://elixir.bootlin.com/linux/v4.18/source/drivers/acpi/bus.c#L783 device looks like it is NULL) With that in mind and with the dmesg logs after "modprobe isl29018": https://pastebin.com/84YzQ0GY I have traced the problem up to the "acpi_primary_dev_companion()" function. I think that that is the one that is returning NULL. Talking with the COREBOOT guys the ACPI asl is correct and they have no idea why the Linux kernel is failing to load that specific device. For reference this is the touchpad dmesg , (as you will see the match is found and the i2c device gets properly probed): https://pastebin.com/PKiTKpD9 I have no more ideas to test out where the problem is. I've tried with different kernel version all 4.18+ If someone has a suggestion/things to help me out with this issue I'm facing it would be welcome. Regards, Nicolò
