Device naming based on device tree

[Thomas De Schampheleire <patrickdepinguin+devicetree-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Hi,

I'm trying to find a proper way for userspace to determine which
devices to talk to. Say you have 4 SPI devices that are registered
against spidev (the userspace SPI handling driver). The device tree
obviously knows which device is which (e.g. a temperature sensor, a
memory device, an actuator, ...) but userspace does not. In the case
of SPI, it sees things like:
    /sys/class/spidev/spidev32766.1/
or worse
    /sys/devices/ffe000000.soc/ffe110000.spi/spi32766.1
but these are too specific.

The same problem occurs for devices using i2c-dev, uio, mtd, ...

For uio, it's possible to determine which device i (i.e. the userspace
program needs to know that a) the device is an SPI devices which by
checking the /sys/class/uio/uioX/name files.
For mtd it is possible to do something similar by strategically
choosing the mtd partition descriptions and creating device nodes or
links based on that information.

Basically, I'm looking for a way to give device tree nodes a name, so
that I can easily access or create devices like /dev/tempsensor0,
/dev/actuator, /dev/serialnum_memory, etc. Ideally such a mechanism is
bus-agnostic: on one board the temperature sensor may be using SPI, on
another I2C.

I assume this is what udev is for, but I'm not sure if it fixes my
problem. In order to name/rename devices with udev, there need to be
rules, and these rules are part of userspace, I cannot dictate them
from the device tree. In an embedded world, you may have three boards
with the same userspace but with different hardware configurations and
thus different device trees.

Are there existing solutions to this problem?
If not, what do you think about such a device-tree-dictated mechanism?

Thanks,
Thomas