I have a devicetree for a custom board with several nodes with no
applicable reg property, such as:
/ {
backlight {
compatible = "pwm-backlight";
};
gpio-keys {
compatible = "gpio-keys";
};
rotary-encoder {
compatible = "rotary-encoder";
};
};
These nodes are then registered as devices with unique names:
$ ls /sys/devices
gpio_keys.8/ rotary_encoder.9/ backlight.6/
... among others.
The uniqueness is guaranteed by of_device_make_bus_id() which uses a global
counter for all nodes with no reg property. The relevant snippet is:
[..]
/*
* No BusID, use the node name and add a globally incremented
* counter (and pray...)
*/
magic = atomic_add_return(1, &bus_no_reg_magic);
dev_set_name(dev, "%s.%d", node->name, magic - 1);
Two nodes can't have the same name and get registered, hence my confusion:
Is the unique number addition absolutely necessary? What am I missing here?
Isn't a bit problematic to register devices with names that depend solely
on probe order (i.e. non-deterministic)?
For instance, hotplug event listeners matching the device name may fail if
the device suddenly change for whatever reason.
Regards,
--
Ezequiel Garcia, VanguardiaSur
www.vanguardiasur.com.ar
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