UIO / of_genirq driver

[John Williams]

Hi,

I came across this thread/patchset from around June last year:

http://lists.ozlabs.org/pipermail/linuxppc-dev/2009-June/073086.html

where Wolfgang proposed a generic OF-driven UIO driver. The
discussion seemed to stall after Grant Likely indicated he didn't like
the use of a linux-specific compatible binding in the device tree
(compatible="generic-uio").

I guess I have a couple of questions:

* did this patchset go anywhere? I've been using it here the last
few days and it works great.

and more generally:

* Is there a better way to handle the OF bindings for this sort of thing?

Grant's complaint seems to come up often - when you have generic
controllers in a system (SPI/I2C also spring to mind), we need a way
of signalling somehow to the kernel that each instance has a
particular usage intended.

However, the device-tree guys complain whenever anyone tries to encode
anything non-hardware related into the DTS itself.

I guess I'd like to just open up a discussion, see if there's been any
progress towards a general solution.

Thanks,

John
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[Wolfram Sang]

John,

> I came across this thread/patchset from around June last year:
>
> http://lists.ozlabs.org/pipermail/linuxppc-dev/2009-June/073086.html
>
> where Wolfgang proposed a generic OF-driven UIO driver. The

Wolfram, please ;)

> discussion seemed to stall after Grant Likely indicated he didn't like
> the use of a linux-specific compatible binding in the device tree
> (compatible="generic-uio").

I agree with him on that.

> I guess I have a couple of questions:
>
> * did this patchset go anywhere? I've been using it here the last
> few days and it works great.

The idea was to create a mechanism to instantiate bindings at runtime, similar
to new_id for PCI/PCMCIA, e.g.:

$ echo "commodore,c64" > /sys/bus/of_platform/drivers/of_uio_genirq/new_compatible

so we don't have to maintain an ever growing list of hardcoded
compatible-properties for those UIO-devices.

> * Is there a better way to handle the OF bindings for this sort of thing?

Run-time instantiation might help in a couple of other cases; still, in the
progress of unifying/extending the OF-support, it was discussed if it was
possible to get rid of of_platform entirely. It looks like a very challenging
task, but seems to be favoured designwise (at least I do).

> However, the device-tree guys complain whenever anyone tries to encode
> anything non-hardware related into the DTS itself.

Well, if I get a device tree including special properties for Linux and BSD and
whatever may follow, that could get quite confusing :)

> I guess I'd like to just open up a discussion, see if there's been any
> progress towards a general solution.

I decided to wait for the outcome of the of_platform-removal-idea. Though, I
have to admit that in the last weeks I haven't followed of-related things due
to other commitments.

Regards,

Wolfram

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[Stefan Roese]

Wolfram,

On Thursday 28 January 2010 11:45:45 Wolfram Sang wrote:
> > I guess I'd like to just open up a discussion, see if there's been any
> > progress towards a general solution.
>
> I decided to wait for the outcome of the of_platform-removal-idea. Though,
> I have to admit that in the last weeks I haven't followed of-related
> things due to other commitments.

Is there any update on this in the meantime? Do you know of any plans to re-
work/-push this patchset? Just checking...

Thanks,
Stefan

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[Wolfram Sang]

> Is there any update on this in the meantime? Do you know of any plans to re-
> work/-push this patchset? Just checking...

I had another look recently; I wouldn't like to just copy/paste the
"new_id"-mechanism from PCI because the code would then exist three
times in the kernel (PCMCIA being the third user I am aware of). I
wondered if it was feasible to make the "new-id"-code generic and make
those subsystems just use it. I haven't started working on it, though.

Kind regards,