Re: [PATCH v7 4/4] iio: light: veml6031x00: add support for events and trigger

On Wed Aug 19, 2026 at 6:42 AM CEST, Andy Shevchenko wrote:
> On Tue, Aug 18, 2026 at 06:10:51PM +0200, Javier Carrasco wrote:
>> On Tue Aug 18, 2026 at 4:01 PM CEST, Andy Shevchenko wrote:
>
> ...
>
>> >> +	ret = pm_runtime_get_if_active(dev);
>> >> +	if (ret <= 0)
>> >
>> > < 0 seems too much to me. If there is disabled runtime PM (and supposedly
>> > device is always on) this prevents from getting events.
>>
>> I am not sure if I get this. A reference is unconditionally acquired
>> when events are enabled as well as in buffer_preenable, and also in the
>> probe before interrupts are enabled. Runtime PM should be active at this
>> point. If not, the interrupt should not come from the device, even if it
>> was on (e.g. before autosuspend kicks in). But maybe I am missing
>>  something?
>
> The device maybe in these states here:
> - powered off (by runtime PM) ret == 0
> - powered on (by some previous activity) ret > 0
> - always on (PM is disabled by user space, for example) ret < 0
>
> Are you telling that the third case is impossible? (Note that autosuspend in
> this case is irrelevant.)
>

I followed the execution paths and the third case seems to be impossible.

Setting power/control to "on" calls pm_runtime_forbid()[1], which sets
runtime_auto to false and increments the usage counter. Note that it does
not update disable_depth, which is the variable that pm_runtime_disable()
updates and what pm_runtime_get_if_active() checks to return -EINVAL if
runtime PM is disabled. Therefore, pm_runtime_get_if_active() should
return a positive value under this configuration.

Nevertheless, I conducted a small experiment to make sure that theory
and praxis match, setting the device to always on and checking what
happens:

# NOTE: These are the first operations on the DUT after booting.
Always on:
$ echo on > /sys/bus/i2c/devices/1-0029/power/control
$ cat /sys/bus/i2c/devices/1-0029/power/control
on

# Low value, so I can easily trigger a rising event with more light:
$ echo 300 > /sys/bus/iio/devices/iio:device0/events/in_illuminance_thresh_rising_value
$ cat /sys/bus/iio/devices/iio:device0/events/in_illuminance_thresh_rising_value
300

# Enable threshold event:
$ echo 1 > /sys/bus/iio/devices/iio:device0/events/in_illuminance_thresh_either_en

# Monitor events:
$ iio_event_monitor /dev/iio:device0

# Good morning! Increment light to trigger the event.
# I instrumented the code to log the value:
[  222.644966] veml6031x00 1-0029: pm_runtime_get_if_active() = 1
# The event:
Event: time: 1773416327710140541, type: illuminance, channel: 0, evtype: thresh, direction: rising
^C

# The configuration is still the one we wanted to test:
$ cat /sys/bus/i2c/devices/1-0029/power/runtime_status
active
cat /sys/bus/i2c/devices/1-0029/power/control
on

[1] https://kernel.org/doc/html/latest/driver-api/pm/devices.html#sys-devices-power-control-files

Best regards,
Javier