Re: (Semi-random) thoughts on device tree structure and devfs

[Matthias Drochner <M.Drochner%fz-juelich.de@localhost>]

plunky%rya-online.net@localhost said:
> > We can discard the pseudo-devices concept, if need be.
> If a device has no parent, just attach it at root (similar to mainbus*),
> with parent == NULL, or even pseudo* at root, and pseudo-dev* at pseudo?

one can do so, but...

> it is not
> possible to pass configuration arguments from userland into the device
> attach routine..

you would set this in stone.
It would be easy to extend the current attach_pseudo() function by
an "attach args" argument. (An interface attribute should be passed
too for consistency because this is used as a qualifier for the
opaque "attach args" elsewhere.)
I think it hasn't been done just because noone needed it.

For the future, I'd think that the currently unstructured "attach args"
needs to be split into 3 parts:
1. Information about the device type, what is needed by child driver's
   "match" function to select the right driver. This is qualified
   by the interface attribute.
2. If the hardware supports it, information about the individual instance,
   as Ethernet HW address, or UUID for disk partitions, to allow drivers
   to recognize a device after temporary disconnection. This is qualified
   by the child device type (which can have multiple attachments).
3. everything else: handles, cookies, whatever needed for parent-child
   communication
For (1), it would make sense to make it a proplist, and pass it to
drvctl, along with locator information, to support on-demand loading
of drivers.

> I think the "pseudo-device" abstraction is unnecessary

I think it makes sense, because it allows to limit use of the
interface-attribute-less "root" to a minimum. There is a reason
that many/most ports use just one "mainbus" at root.

best regards
Matthias




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