On Friday 27 February 2009, Ira Snyder wrote:

On Thu, Feb 26, 2009 at 11:34:33PM +0100, Arnd Bergmann wrote:

quoted

I guess the best option for doing it in Linux then would be to have
a board control driver (not sure if this already exists) that exports
high-level functions to set up the inbound and outbound windows.

Nothing like it exists. The OF device tree doesn't even describe these
registers. The code in arch/powerpc/sysdev/fsl_pci.c uses some registers
near these, but it gets their address by masking the low bits off the
addresses from the device tree and adding the offsets of the new
registers. Nasty.

I'll do this for now:
1) Get the message unit registers from my device tree
2) Encapsulate all use of get_immrbase() to a single function

That way it could be easily replaced in the future when something more
suitable comes along.

Ok. However, I don't expect this to get fixed magically. Ideally,
you would start a new file for the board control in arch/powerpc/sysdev
and export the function from there, otherwise you do it the way you
suggested.
Then we can tell the fsl_pci and other people to use the same
method and source file to access the board control.

I didn't think about this at all. This driver could be used to boot a
(guest) system over NFS, so in that case there isn't a userspace running
yet, to allow configuration. This is essentially my use case, though I
haven't implemented it yet.

Also, I hate designing user interfaces :) Any concrete suggestions on
design would be most welcome.

Don't worry about it for now, just put all the hardcoded virtio_net
specific stuff into a file separate from the hardware specific
files so that we have a nice kernel level abstraction to build a
user abstraction on top of.

	Arnd <><